drm/ingenic: Fix leak of device_node pointer

of_graph_get_remote_node() requires of_node_put() to be called on the
device_node pointer when it's no more in use.

Fixes: fc1acf31 ("drm/ingenic: Add support for the IPU")
Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20200827114404.36748-1-paul@crapouillou.net