MIPS: generic: fix missing of_node_put()

of_find_compatible_node() returns a device_node pointer with refcount
incremented and must be decremented explicitly.
 As this code is using the result only to check presence of the interrupt
controller (!NULL) but not actually using the result otherwise the
refcount can be decremented here immediately again.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Signed-off-by: Paul Burton <paul.burton@mips.com>
Patchwork: https://patchwork.linux-mips.org/patch/19820/
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: James Hogan <jhogan@kernel.org>
Cc: linux-mips@linux-mips.org
Cc: linux-kernel@vger.kernel.org