media: imx: imx7_mipi_csis: Runtime suspend in .s_stream() error path

If the .s_stream() handler fails after calling pm_runtime_get_sync(),
call pm_runtime_put() in the error path.

While at it add a few blank lines to make the code more readable.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Rui Miguel Silva <rmfrfs@gmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>