ALSA: usb-audio: parse UAC2 sample rate ranges correctly

A device may report its supported sample rates in ranges rather than in
discrete triplets. The code used to only parse the MIN field instead of
properly paying attention to the MAX and RES values.

Also, handle RES values of 1 correctly and announce a continous sample
rate range in this case.

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Reported-by: Alex Lee <alexlee188@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>