sm501fb: RGB offsets are reversed in 16bpp modes

The RGB offsets were reversed in 16bpp modes.  Simply trying to reverse the
offsets when endianness differs is clearly the wrong thing to do but that is
an issue for another patch.

Signed-off-by: Ville Syrjala <syrjala@sci.fi>
Acked-by: Ben Dooks <ben-linux@fluff.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>