ARM: hisi: fix error handling and missing of_node_put

of_iomap() can return NULL which seems critical here and thus should be
explicitly flagged so that the cause of system halting can be understood.
As of_find_compatible_node() is returning a device node with refcount
incremented it must be explicitly decremented here.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Fixes: commit 7fda91e7 ("ARM: hisi: enable smp for HiP01")
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>