ALSA: line6: Pass driver name to line6_probe()

Provide a unique name for each driver instead of using "line6usb" for
all of them.  This will allow for different configurations based on the
driver type.

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