video: st7735fb: Correct colors for black-tab version of st7735 board

New version of st7735 board from adafruit (black tab) needs to
have 'R' and 'B' swapped before sending to SPI controller.

Referred to adafruit library [1]

TODO: DT property has to be used to differentiate these displays
from the older variants.

[1] https://github.com/adafruit/Adafruit-ST7735-Library/commit/3d868aff975d0eb39e4689b687f0a1952f6140a2

Signed-off-by: Joel Fernandes <joelf@ti.com>