media: stm32: csi: add missing pm_runtime_put on error

Within the stm32_csi_start function, pm_runtime_put should
be called upon error following pm_runtime_get_sync.
Rework the function error handling by putting a label in
order to have common error handling for all calls requiring
pm_runtime_put.

Signed-off-by: Alain Volmat <alain.volmat@foss.st.com>
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>