media: stm32-dcmi: add mandatory of_node_put() in success path

The endpoint allocated by of_graph_get_next_endpoint() needs an of_node_put()
in both error and success path. As  ep  is not used the refcount decrement
can be right after the last use of  ep.

Fixes: commit 37404f91 ("[media] stm32-dcmi: STM32 DCMI camera interface driver")

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>