Update MFRC522.cpp

[rapi3]

Description: Extend range for MFRC522 RFID Reader. Set RFCfgReg to 48db gain

Related issue (if applicable): fixes #

Checklist:

• The pull request is done against the latest development branch
• Only relevant files were touched
• Only one feature/fix was added per PR and the code change compiles without warnings
• The code change is tested and works on Tasmota core ESP8266 V.2.7.4.9
• The code change is tested and works on Tasmota core ESP32 V.1.0.5-rc6
• I accept the CLA.

NOTE: The code change must pass CI tests. Your PR cannot be merged unless tests pass

[Jason2866]

Increasing sensitivity normally results in decreasing accuracy (in decoding).
Have you tested how this change affects near range detection?

[rapi3]

yes I have and I am testing in the last days:

• without this change the range it is very low on my reader ~0.5-1cm, I almost have to touch the cards to antenna and I don't think it is possible to have the reader in a case and use it for a real project attached to a door without RFCfgReg increased.
• with change RFCfgReg increased the range it is ~3 cm and I don't see any problem.
  It will be nice in the future to have availability SetOptions for this parameter, bu that will require a lot of work from you.

p.s.
I just found another project that have the option to change this parameter like SetOptions in Tasmota and I also don't see any problems with accuracy as I am also testing:
https://github.com/esprfid/esp-rfid

[arendst]

Implemented using command Sensor80 1 <0..7> where 0 to 7 see below: