x86, realmode: Fix always-zero test in reboot_32.S

A test instruction is an "and", and an and with zero is always zero.
This would cause us to always take the BIOS path, not the APM path, in
case anyone actually cares...

Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Link: http://lkml.kernel.org/r/1336501366-28617-17-git-send-email-jarkko.sakkinen@intel.com