ARM: hisi: handle of_iomap and fix missing of_node_put

Relying on an unchecked of_iomap() which can return NULL is problematic
here, an explicit check seems mandatory. Also the call to
of_find_compatible_node() returns a device node with refcount incremented
therefor an explicit of_node_put() is needed here.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Fixes: commit 22bae429 ("ARM: hi3xxx: add hotplug support")
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>