ALSA: usb-audio: add support for wireless USB devices

This patch updates snd_usb_audio_create also support devices whose
speed == USB_SPEED_WIRELESS.

Signed-off-by: Thomas Pugliese <thomas.pugliese@gmail.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>