ALSA: usb-audio: Add skip_validation option

ALSA: usb-audio: Add skip_validation option

The unit descriptor validation may lead to a probe error when the
device provides a buggy descriptor or the validator detected
incorrectly.  For identifying such an error and band-aiding, give a
new module option, skip_validation.  With this option, the driver
ignores the validation errors with the hexdump of the unit
descriptor, so we can check it in a bit more details.

Link: https://lore.kernel.org/r/20191114165613.7422-2-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>