xtensa: fix section mismatch in pcibios_fixup_bus

Remove __init annotation from pcibios_fixup_bus as is called from
pci_scan_child_bus which is not __init.

Also fix a couple of minor build warnings.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Signed-off-by: Chris Zankel <chris@zankel.net>