[Silabs][SiWx917] Fixing uart to read only once

[chirag-silabs]

Uart read was called twice causing to enter the character twice to register in tera term.
fixed the read so that the read event is not called twice.

Tested locally

[github-actions]

PR #25902: Size comparison from 21aa4d6 to 110cffd

Decreases (1 build for cc32xx)

platform	target	config	section	21aa4d6	110cffd	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL	.debug_info	20310044	20310043	-1	-0.0

Full report (1 build for cc32xx)

platform	target	config	section	21aa4d6	110cffd	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL		0	0	0	0.0
			(read only)	645769	645769	0	0.0
			(read/write)	203848	203848	0	0.0
			.ARM.attributes	44	44	0	0.0
			.ARM.exidx	8	8	0	0.0
			.bss	197248	197248	0	0.0
			.comment	194	194	0	0.0
			.data	1480	1480	0	0.0
			.debug_abbrev	933102	933102	0	0.0
			.debug_aranges	87704	87704	0	0.0
			.debug_frame	301596	301596	0	0.0
			.debug_info	20310044	20310043	-1	-0.0
			.debug_line	2681003	2681003	0	0.0
			.debug_loc	2827360	2827360	0	0.0
			.debug_ranges	286352	286352	0	0.0
			.debug_str	3041144	3041144	0	0.0
			.ramVecs	780	780	0	0.0
			.resetVecs	64	64	0	0.0
			.rodata	105953	105953	0	0.0
			.shstrtab	232	232	0	0.0
			.stab	204	204	0	0.0
			.stabstr	441	441	0	0.0
			.stack	2048	2048	0	0.0
			.strtab	380543	380543	0	0.0
			.symtab	257472	257472	0	0.0
			.text	537696	537696	0	0.0

[github-actions]

PR #25902: Size comparison from d81d4e3 to 2a63a59

Increases (1 build for cc32xx)

platform	target	config	section	d81d4e3	2a63a59	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL	.debug_info	20302987	20302988	1	0.0

Full report (4 builds for cc32xx, mbed, qpg)

platform	target	config	section	d81d4e3	2a63a59	change	% change
cc32xx	lock	CC3235SF_LAUNCHXL		0	0	0	0.0
			(read only)	644409	644409	0	0.0
			(read/write)	203848	203848	0	0.0
			.ARM.attributes	44	44	0	0.0
			.ARM.exidx	8	8	0	0.0
			.bss	197248	197248	0	0.0
			.comment	194	194	0	0.0
			.data	1480	1480	0	0.0
			.debug_abbrev	933099	933099	0	0.0
			.debug_aranges	87608	87608	0	0.0
			.debug_frame	301328	301328	0	0.0
			.debug_info	20302987	20302988	1	0.0
			.debug_line	2679748	2679748	0	0.0
			.debug_loc	2824679	2824679	0	0.0
			.debug_ranges	286200	286200	0	0.0
			.debug_str	3039406	3039406	0	0.0
			.ramVecs	780	780	0	0.0
			.resetVecs	64	64	0	0.0
			.rodata	105953	105953	0	0.0
			.shstrtab	232	232	0	0.0
			.stab	204	204	0	0.0
			.stabstr	441	441	0	0.0
			.stack	2048	2048	0	0.0
			.strtab	377422	377422	0	0.0
			.symtab	256768	256768	0	0.0
			.text	536336	536336	0	0.0
mbed	lock-app	CY8CPROTO_062_4343W+release	(read only)	6224	6224	0	0.0
			(read/write)	2466152	2466152	0	0.0
			.bss	215964	215964	0	0.0
			.data	5880	5880	0	0.0
			.text	1428796	1428796	0	0.0
qpg	lighting-app	qpg6105+debug	(read/write)	1153680	1153680	0	0.0
			.bss	97404	97404	0	0.0
			.data	852	852	0	0.0
			.text	600776	600776	0	0.0
	lock-app	qpg6105+debug	(read/write)	1122216	1122216	0	0.0
			.bss	92540	92540	0	0.0
			.data	856	856	0	0.0
			.text	569316	569316	0	0.0