This makes sure f_midi doesn't try to enqueue data when the IN endpoint is
disabled, ie, USB cable is disconnected.
Reviewed-by: NRobert Baldyga <r.baldyga@samsung.com>
Signed-off-by: NFelipe F. Tonello <eu@felipetonello.com>
Signed-off-by: NFelipe Balbi <balbi@ti.com>