x86, efi: Fix PCI ROM handing in EFI boot stub, in 32-bit mode

The 'Attributes' argument to pci->Attributes() function is 64-bit. So
when invoking in 32-bit mode it takes two registers, not just one.

This fixes memory corruption when booting via the 32-bit EFI boot stub.

Signed-off-by: David Woodhouse <David.Woodhouse@intel.com>
Cc: <stable@kernel.org>
Link: http://lkml.kernel.org/r/1358513837.2397.247.camel@shinybook.infradead.org
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
Cc: Matt Fleming <matt.fleming@intel.com>