[POWERPC] free_property() must not be __init

This fixes the following section mismatch:

<--  snip  -->

...
WARNING: vmlinux.o(.text+0x55648): Section mismatch in reference from the function .free_node() to the function .init.text:.free_property()
...

<--  snip  -->

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Acked-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Paul Mackerras <paulus@samba.org>