USB: gadget: section mismatch warning fixed

In may gadgets bind and bind like functions were in a init section
as they were only run during initialisation.  However, being
callback functions they were referenced from structures in “normal”
sections.  Changing the tag from “__init” to “__ref” fixes the
warnings.

Signed-off-by: Michal Nazarewicz <m.nazarewicz@samsung.com>
Cc: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>