media: ov7251: Fix multiple problems in s_stream callback

The s_stream callback had several issues:

- If pm_runtime_get_sync() fails, the usage_count is not put.

- The sensor wasn't suspended if s_stream(subdev, 1) failed.

Fix this.

Fixes: ("media: i2c: Add pm_runtime support to ov7251")
Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>