x86/simplefb: Use PTR_ERR_OR_ZERO

Replace IS_ERR/PTR_ERR

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Link: http://lkml.kernel.org/r/1413576066-26925-1-git-send-email-fabf@skynet.be


Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>