mmc: sdhci-of-esdhc: Fix refcount leak in esdhc_signal_voltage_switch

of_find_matching_node() returns a node pointer with refcount
incremented, we should use of_node_put() on it when not need anymore.
Add missing of_node_put() to avoid refcount leak.
of_node_put() checks null pointer.

Fixes: ea35645a

 ("mmc: sdhci-of-esdhc: add support for signal voltage switch")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Link: https://lore.kernel.org/r/20220523144255.10310-1-linmq006@gmail.com
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>