ALSA: usb-audio: Add clock validity quirk for Denon MC7000/MCX8000

It should be safe to ignore clock validity check result if the following
conditions are met:
 - only one single sample rate is supported;
 - the terminal is directly connected to the clock source;
 - the clock type is internal.

This is to deal with some Denon DJ controllers that always reports that
clock is invalid.

Tested-by: Tobias Oszlanyi <toszlanyi@yahoo.de>
Signed-off-by: Alexander Tsoy <alexander@tsoy.me>
Cc: <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/20200212235450.697348-1-alexander@tsoy.me


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