ALSA: usb-audio: UAC3: Parse Input Terminal number of channels.

Obtain the number of channels for the Input Terminal from the
Logical Cluster Descriptor. This achieves a useful minimal parsing
of this unit so it can be used in other units in the topology.

Signed-off-by: Jorge Sanjuan <jorge.sanjuan@codethink.co.uk>
Reviewed-by: Ruslan Bilovol <ruslan.bilovol@gmail.com>
Tested-by: Ruslan Bilovol <ruslan.bilovol@gmail.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>