ALSA: usb-audio: Fix some typos

Fix the following typos in comments and in the code:
 - KHz -> kHz
 - procssed -> processed

Signed-off-by: Alexander Tsoy <alexander@tsoy.me>
Link: https://lore.kernel.org/r/20200629032607.255419-1-alexander@tsoy.me


Signed-off-by: Takashi Iwai <tiwai@suse.de>