ALSA: line6: snd-usb-line6 depends on CONFIG_SND_HWDEP

ERROR: "snd_hwdep_new" [sound/usb/line6/snd-usb-line6.ko] undefined!
scripts/Makefile.modpost:91: recipe for target '__modpost' failed
make[1]: *** [__modpost] Error 1

Fixes: a16039cb ('ALSA: line6: Add hwdep interface to access the POD control messages')
Signed-off-by: Valdis Kletnieks <valdis.kletnieks@vt.edu>
Reviewed-by: Takashi Sakamoto <o-takashi@sakamocchi.jp>
Signed-off-by: Takashi Iwai <tiwai@suse.de>