ALSA: usb-audio: don't try to get Outlaw RR2150 sample rate

This quirk allows us to avoid the noisy:

	current rate 0 is different from the runtime rate

message every time playback starts.  While USB DAC in the RR2150
supports reading the sample rate, it never returns a sample rate
other than zero in my observation with common sample rates.

Signed-off-by: Eric Wong <normalperson@yhbt.net>
Cc: Joe Turner <joe@oampo.co.uk>
Cc: <stable@vger.kernel.org>
Signed-off-by: Takashi Iwai <tiwai@suse.de>