mmc: atmel-mci: add missing of_node_put

for_each_child_of_node performs an of_node_get on each
iteration, so a break out of the loop requires an
of_node_put.

This was done using the Coccinelle semantic patch
iterators/for_each_child.cocci

Signed-off-by: Julia Lawall <Julia.Lawall@inria.fr>
Link: https://lore.kernel.org/r/20230907095521.14053-6-Julia.Lawall@inria.fr
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>