Input: mtk-pmic-keys - add of_node_put() before return

Each iteration of for_each_child_of_node puts the previous
node, but in the case of a return from the middle of the loop, there is
no put, thus causing a memory leak. Hence add an of_node_put before the
return in three places.
Issue found with Coccinelle.

Signed-off-by: Nishka Dasgupta <nishkadg.linux@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>