ALSA: usb-audio: fix Fast Track Ultra (8R) 44.1 sample rates

The M-Audio Fast Track Ultra series devices did not play sound correctly
at 44.1/88.2 kHz. Changing the output endpoint attribute to adaptive
fixes this.

Signed-off-by: Felix Homann <fexpop@web.de>
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>