ALSA: usb-audio: Don't start stream for capture at prepare

ALSA: usb-audio: Don't start stream for capture at prepare

commit 50d06d1d4490db2f2637419f5ca77358cad3187c upstream.

The recent change made mistakenly the stream for capture started at
prepare stage.  Add the stream direction check to avoid it.

Fixes: 0b78bb8fcbed ("ALSA: usb-audio: Rename early_playback_start flag with lowlatency_playback")
Link: https://lore.kernel.org/r/20211119102629.7476-1-tiwai@suse.de
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>