USB USX2Y
Return -EBUSY from snd_usX2Y_usbpcm_open(), if the associated hwdep
device is not opened.

It now works as originally intended. Had forgotten a pair of parenthesis.
Signed-off-by: Karsten Wiese <annabellesgarden@yahoo.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>