x86, efi: fix 32-bit warnings in setup_efi_pci()

Fix four similar build warnings on 32-bit (casts between different
size pointers and integers).

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Stefan Hasko <hasko.stevo@gmail.com>
Signed-off-by: Matt Fleming <matt.fleming@intel.com>