usb: gadget: free opts struct on error recovery

Fix memory leaks introduced in commits:

40d133d7
usb: gadget: f_ncm: convert to new function interface with backward compatibility

fee562a6
usb: gadget: f_ecm: convert to new function interface with backward compatibility

fcbdf12e
usb: gadget: f_phonet: convert to new function interface with backward compatibility

b29002a1
usb: gadget: f_eem: convert to new function interface with backward compatibility

8cedba7c
usb: gadget: f_subset: convert to new function interface with backward compatibility

f466c635
usb: gadget: f_rndis: convert to new function interface with backward compatibility

Acked-by: Michal Nazarewicz <mina86@mina86.com>
Signed-off-by: Andrzej Pietrasiewicz <andrzej.p@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>