ALSA: usb-audio: Fix Scarlett 6i6 initialization typo

The num_controls field was incorrectly set to 0 causing 6i6 to not be
initialized. Set this to 9.
Reported-and-tested-by: Mark Roberts <sunifiram@gmail.com>
Signed-off-by: Chris J Arges <chris.j.arges@canonical.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/mixer_scarlett.c

@@ -655,7 +655,7 @@ static struct scarlett_device_info s6i6_info = {
 		.names = NULL
 	},
 
-	.num_controls = 0,
+	.num_controls = 9,
 	.controls = {
 		{ .num = 0, .type = SCARLETT_OUTPUTS, .name = "Monitor" },
 		{ .num = 1, .type = SCARLETT_OUTPUTS, .name = "Headphone" },