media: v4l2-dev: fix error handling in __video_register_device()

Once device_register() failed, we should call put_device() to
decrement reference count for cleanup. Or it could cause memory leak.
And move callback function v4l2_device_release() and v4l2_device_get()
before put_device().

As comment of device_register() says, 'NOTE: _Never_ directly free
@dev after calling this function, even if it returned an error! Always
use put_device() to give up the reference initialized in this function
instead.'

Found by code review.

Cc: stable@vger.kernel.org
Fixes: dc93a70c ("V4L/DVB (9973): v4l2-dev: use the release callback from device instead of cdev")
Signed-off-by: Ma Ke <make24@iscas.ac.cn>
Reviewed-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Hans Verkuil <hverkuil@xs4all.nl>