media: uvcvideo: Handle control pipe protocol STALLs

When a command ends up in a STALL on the control pipe, use the Request
Error Code control to provide a more precise error information to the
user. For example, if a camera is still busy processing a control,
when the same or an interrelated control set request arrives, the
camera can react with a STALL and then return the "Not ready" status
in response to a UVC_VC_REQUEST_ERROR_CODE_CONTROL command. With this
patch the user would then get an EBUSY error code instead of a
generic EPIPE.

Signed-off-by: Guennadi Liakhovetski <guennadi.liakhovetski@intel.com>
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>