Do not overwrite bits which contain memory type settings.  It removes
noise pixels ("snow") on Blade3D and 3DImage chips.
Signed-off-by: NKrzysztof Helt <krzysztof.h1@wp.pl>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>