Input: xpad - factor out URB submission in xpad_play_effect

Move submission logic to a single point at the end of the function.
This makes it easy to add locking/ queuing code later on.

Signed-off-by: Pavel Rojtberg <rojtberg@gmail.com>
Signed-off-by: Dmitry Torokhov <dmitry.torokhov@gmail.com>