ALSA: usb-audio: Handle error for the current selector gracefully

Currently we bail out when the device returns an error or an invalid
value for the current clock selector value via
uac_clock_selector_get_val().  But it's possible that the device is
really uninitialized and waits for the setup of the proper route at
first.

For handling such a case, this patch lets the driver dealing with the
error or the invalid error more gracefully, choosing the clock source
automatically instead.

Link: https://lore.kernel.org/r/20210518152112.8016-3-tiwai@suse.de


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