parisc: add missing __init annotation

parisc: add missing __init annotation

compilation failed with:

MODPOST vmlinux.o
WARNING: vmlinux.o(.text.unlikely+0xa0c): Section mismatch in reference from the function walk_lower_bus() to the function .init.text:walk_native_bus()
The function walk_lower_bus() references
the function __init walk_native_bus().
This is often because walk_lower_bus lacks a __init
annotation or the annotation of walk_native_bus is wrong.

FATAL: modpost: Section mismatches detected.
Set CONFIG_SECTION_MISMATCH_WARN_ONLY=y to allow them.
make[2]: *** [/home/svens/linux/parisc-linux/src/scripts/Makefile.modpost:64: __modpost] Error 1
make[1]: *** [/home/svens/linux/parisc-linux/src/Makefile:1077: vmlinux] Error 2
make[1]: Leaving directory '/home/svens/linux/parisc-linux/build'
make: *** [Makefile:179: sub-make] Error 2

Signed-off-by: Sven Schnelle <svens@stackframe.org>
Signed-off-by: Helge Deller <deller@gmx.de>