x86emu: Use NULL instead of 0 when assigning pointer

Change-Id: Ie79b9aa79d45dd10c2e5be7f58eed970c243060a
Signed-off-by: Stefan Reinauer <reinauer@google.com>
Reviewed-on: http://review.coreboot.org/1361
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>
1 file changed