regulator: add missing call to of_node_put()

In one of the error paths of the for_each_child_of_node() loop,
add missing call to of_node_put().

Fix the following coccicheck warning:
./drivers/regulator/scmi-regulator.c:343:1-23: WARNING: Function
"for_each_child_of_node" should have of_node_put() before return around
line 347.

Reported-by: Abaci Robot <abaci@linux.alibaba.com>
Signed-off-by: Yang Li <yang.lee@linux.alibaba.com>
Link: https://lore.kernel.org/r/1614303575-27436-1-git-send-email-yang.lee@linux.alibaba.com
Signed-off-by: Mark Brown <broonie@kernel.org>