[media] v4l2-ioctl: allow all controls if ctrl_class == 0

The check_ext_ctrls() function in v4l2-ioctl.c checks if all controls in the
control array are from the same control class as c->ctrl_class. However,
that check should only be done if c->ctrl_class != 0. A 0 value means
that this restriction does not apply.

So return 1 (OK) if c->ctrl_class == 0.

Found by running v4l2-compliance on the uvc driver.

Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Acked-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@osg.samsung.com>