efifb: fix int to pointer cast warning

drivers/video/efifb.c:247: warning: cast to pointer from integer of different size

Signed-off-by: Konstantin Khlebnikov <khlebnikov@openvz.org>
Signed-off-by: Peter Jones <pjones@redhat.com>
Signed-off-by: Paul Mundt <lethal@linux-sh.org>