of: reserved_mem: add missing of_node_put() for proper ref-counting

Commit d698a388 ("of: reserved-memory: ignore disabled memory-region
nodes") added an early return in of_reserved_mem_device_init_by_idx(), but
didn't call of_node_put() on a device_node whose ref-count was incremented
in the call to of_parse_phandle() preceding the early exit.

Fixes: d698a388 ("of: reserved-memory: ignore disabled memory-region nodes")
Change-Id: I293be0fb7f86a1e6e4d4d7277039a881e590d5e0
Signed-off-by: Chris Goldsworthy <cgoldswo@codeaurora.org>