ALSA: line6: Let snd_card_new() allocate private data

Instead of allocating the private data individually in each driver's
probe at first, let snd_card_new() allocate the data that is called in
line6_probe().  This simplifies the primary probe functions.

Tested-by: Chris Rorvick <chris@rorvick.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>

sound/usb/line6/driver.h

@@ -181,9 +181,9 @@ extern int line6_write_data(struct usb_line6 *line6, int address, void *data,
 
 int line6_probe(struct usb_interface *interface,
 		const struct usb_device_id *id,
-		struct usb_line6 *line6,
 		const struct line6_properties *properties,
-		int (*private_init)(struct usb_line6 *, const struct usb_device_id *id));
+		int (*private_init)(struct usb_line6 *, const struct usb_device_id *id),
+		size_t data_size);
 
 void line6_disconnect(struct usb_interface *interface);