msm_fb: Correct R and G offsets for correct mapping

R and G colors are swapped when ARGC test cases are executed.
Correct the color mapping to right register offset to fix
the color swapping issue.

CRs-Fixed: 491215

Change-Id: I4997acce577bdbbdf39e22502a678dbecf0bfc37
Signed-off-by: Jeevan Shriram <jshriram@codeaurora.org>