ALSA: usb-audio: Put missing KERN_CONT prefix

The usb-audio driver has a debug printk code without proper KERN_
prefix.  On recent kernels, KERN_CONT prefix is mandatory for
continued output lines.  Put it properly.
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/midi.c

@@ -242,8 +242,8 @@ static void dump_urb(const char *type, const u8 *data, int length)
 {
 	snd_printk(KERN_DEBUG "%s packet: [", type);
 	for (; length > 0; ++data, --length)
-		printk(" %02x", *data);
-	printk(" ]\n");
+		printk(KERN_CONT " %02x", *data);
+	printk(KERN_CONT " ]\n");
 }
 #else
 #define dump_urb(type, data, length) /* nothing */