ALSA: usx2y: Add sanity checks for invalid EPs

usx2y driver sets up URBs containing the fixed endpoints without
validation.  This may end up with an oops-like kernel warning when
submitted.

For avoiding it, this patch adds the calls of the new sanity-check
helper for URBs.

Signed-off-by: Takashi Iwai <tiwai@suse.de>