powerpc/pci: Fix annotation of pcibios_claim_one_bus

It was __devinit, but it is also within a CONFIG_HOTPLUG guarded section
of code, so the __devinit does nothing but cause the following warning:

WARNING: vmlinux.o(.text+0x107a8): Section mismatch in reference from the function pcibios_finish_adding_to_bus() to the function .devinit.text:pcibios_claim_one_bus()
The function pcibios_finish_adding_to_bus() references
the function __devinit pcibios_claim_one_bus().
This is often because pcibios_finish_adding_to_bus lacks a __devinit
annotation or the annotation of pcibios_claim_one_bus is wrong.

It is also only (externally) used in arch/powerpc/kernel/of_platform.c
which cannot be built as a module so don't export it.

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>