separate handling of red and blue color balance

[wherget]

(this is an issue submitted by [vogarth] on the showmewebcam Discord)

Expected Behavior

UVC control WHITE_BALANCE_COMPONENT can affect both V4L2_CID_RED_BALANCE and V4L2_CID_BLUE_BALANCE independently.

Current Behavior

(my analysis from reading code, not [vogarth]'s).
V4L2_CID_RED_BALANCE and V4L2_CID_BLUE_BALANCE are both set to the value of V4L2_CID_RED_BALANCE

This affects both master and feat/new-code.

Possible Solution

AFAICS the UVC control sends two bytes (red/blue separately) as control value, and v4l2_set_ctrl only receives a single int, which it sets for both channels. There should probably be some additional handling for handling multi-byte UVC controls.