rt->rate is an unsigned char so it's never equal to -1.  It's not a huge
problem because the invalid rate is caught inside the call to
usb6fire_pcm_set_rate() which returns -EINVAL.  But if we fix the test
then it prints out the correct error message so that's good.
Signed-off-by: NDan Carpenter <error27@gmail.com>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>

What is working: Everything except SPDIF
- Hardware Master volume
- PCM 44-192kHz@24 bits, 6 channels out, 4 channels in (analog)
- MIDI in/out
- firmware loading after cold start
- phono/line switching
Signed-off-by: NTorsten Schenk <torsten.schenk@zoho.com>
Signed-off-by: NTakashi Iwai <tiwai@suse.de>