usb: gadget: f_uac1: stop playback on function disable

usb: gadget: f_uac1: stop playback on function disable

There is missing playback stop/cleanup in case of
gadget's ->disable callback that happens on
events like USB host resetting or gadget disconnection

Fixes: 368346a9ad12 ("usb: gadget: add f_uac1 variant based on a new u_audio api")
Cc: <stable@vger.kernel.org> # 4.13+
Signed-off-by: Ruslan Bilovol <ruslan.bilovol@gmail.com>
Link: https://lore.kernel.org/r/1614599375-8803-3-git-send-email-ruslan.bilovol@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>