mmc: mmci: Fix device_node reference leak in of_get_dml_pipe_index()

mmc: mmci: Fix device_node reference leak in of_get_dml_pipe_index()

When calling of_parse_phandle_with_args(), the caller is responsible
to call of_node_put() to release the reference of device node.
In of_get_dml_pipe_index(), it does not release the reference.

Fixes: 9cb15142d0e3 ("mmc: mmci: Add qcom dml support to the driver.")
Signed-off-by: Felix Gu <gu_0233@qq.com>
Cc: stable@vger.kernel.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>