ALSA: usb-audio: Pass JOINT_DUPLEX info flag for implicit fb streams

When a stream is in the implicit feedback mode, it's more or less tied
with a capture stream.  Passing SNDRV_PCM_INFO_JOINT_DUPLEX may help
for user-space to understand the situation.

Link: https://lore.kernel.org/r/20211007083528.4184-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>