[PATCH] savagefb: X-panning fixes

The driver unconditionally sets xpanstep to 2.  However, a value of 4
empirically works better at bpp = 8, and 2 for 16 and 32.  This buglet was
exposed by the rotation code.

Second fix is the unconditional call to update_start() without verifying if
the offsets are correct.  Remove this call, it's not necessary and secondly,
it causes a crash with invalid values.

Signed-off-by: Antonino Daplas <adaplas@pol.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>