ARM: ux500: add missing of_node_put()

 of_find_compatible_node() returns a pointer with refcount incremented
so both in the error path as well as after usage in soc_info_populate()
respectively actually b8500_read_soc_id() an explicit of_node_put is
needed to release backupram.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Fixes: commit 18a99278 ("ARM: ux500: move soc_id driver to drivers/soc")
Acked-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>