drm: sis fix compile warning

Prevent a gcc warning in the SIS DRM driver.  offset is a unsigned int and
the printk wants a long.

Signed-off-by: Jon Mason <jdmason@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Dave Airlie <airlied@linux.ie>