PCI: Make pcibios_add_platform_entries() return errors

Currently pcibios_add_platform_entries() returns void, but could fail,
so instead have it return an int and propagate errors up to
pci_create_sysfs_dev_files().

Fixes:
arch/powerpc/kernel/pci_64.c: In function 'pcibios_add_platform_entries':
arch/powerpc/kernel/pci_64.c:878: warning: ignoring return value of
	'device_create_file', declared with attribute warn_unused_result
arch/powerpc/kernel/pci_32.c: In function 'pcibios_add_platform_entries':
  arch/powerpc/kernel/pci_32.c:1043: warning: ignoring return value of
	'device_create_file', declared with attribute warn_unused_result

Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>