sparc64: fix compile warning section mismatch in find_node()

A compile warning is introduced by a commit to fix the find_node().
This patch fix the compile warning by moving find_node() into __init
section. Because find_node() is only used by memblock_nid_range() which
is only used by a __init add_node_ranges(). find_node() and
memblock_nid_range() should also be inside __init section.

Signed-off-by: Thomas Tai <thomas.tai@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>