ALSA: usb-audio: Fix potential memory leaks

ALSA: usb-audio: Fix potential memory leaks

When the driver hits -ENOMEM at allocating a URB or a buffer, it
aborts and goes to the error path that releases the all previously
allocated resources.  However, when -ENOMEM hits at the middle of the
sync EP URB allocation loop, the partially allocated URBs might be
left without released, because ep->nurbs is still zero at that point.

Fix it by setting ep->nurbs at first, so that the error handler loops
over the full URB list.

Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20220930100151.19461-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>