HID Bootloader watchdog improvements

[NicoHood]

From my old fixes I still found this one open:
NicoHood/SecureLoader@afda49c

It seems to be still okay. I think I've added this special attribute to the variable to safe ram or to compile properly. Have not tested it again, but worked at that time of course.

Background: Watchdog will always get disabled, so dont do it twice. Safe the register value to process it later. I think this is also better, as it disables the watchdog even faster.