media: exynos4-is: fix leaked of_node references

The call to of_get_child_by_name returns a node pointer with refcount
incremented thus it must be explicitly decremented after the last
usage.

Detected by coccinelle with the following warnings:
drivers/media/platform/exynos4-is/fimc-is.c:813:2-8: ERROR: missing of_node_put; acquired a node pointer with refcount incremented on line 807, but without a corresponding object release within this function.
drivers/media/platform/exynos4-is/fimc-is.c:870:1-7: ERROR: missing of_node_put; acquired a node pointer with refcount incremented on line 807, but without a corresponding object release within this function.
drivers/media/platform/exynos4-is/fimc-is.c:885:1-7: ERROR: missing of_node_put; acquired a node pointer with refcount incremented on line 807, but without a corresponding object release within this function.
drivers/media/platform/exynos4-is/media-dev.c:545:1-7: ERROR: missing of_node_put; acquired a node pointer with refcount incremented on line 541, but without a corresponding object release within this function.
drivers/media/platform/exynos4-is/media-dev.c:528:1-7: ERROR: missing of_node_put; acquired a node pointer with refcount incremented on line 499, but without a corresponding object release within this function.
drivers/media/platform/exynos4-is/media-dev.c:534:1-7: ERROR: missing of_node_put; acquired a node pointer with refcount incremented on line 499, but without a corresponding object release within this function.

Signed-off-by: Wen Yang <wen.yang99@zte.com.cn>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>