usb: gadget: printer: use after free in gprinter_alloc_inst()

There was a missing goto so we free "opts" and then dereference it.

Fixes: ee1cd515 ('usb: gadget: printer: add configfs support')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>