USB: musb: fix put_device() call sequence

Invoke put_device(musb->xceiv->dev) before musb_platform_exit()as
xceiv is getting unregistered in musb_platform_exit().

Fixes put_device() panic when module insert/removal is performed
multiple times.

Signed-off-by: Ajay Kumar Gupta <ajay.gupta@ti.com>
Acked-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>