i810fb: fix incorrect frequency mask

Fix a long-standing bug.  The mask used to detect a 100Mhz or 133Mhz chipset
is incorrect. (The only side effect of this bug is that it will choose an
incorrect watermark).

Signed-off-by: Antonino Daplas <adaplas@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>