gralloc: Fix inverted colors on BRGA

Don't assume any 32bpp mode is RGBX.
This is a forward-port of
commit f50b075a8b88eff482628e8ab62a04539117c7ea

Signed-off-by: Bernhard Rosenkraenzer <Bernhard.Rosenkranzer@linaro.org>
1 file changed