USB: gadget: fix up const issue with struct usb_function_instance

In struct usb_function, the struct usb_function_instance pointer
variable "fi" is listed as const, but it is written to in numerous
places, making the const marking of it a total lie. Fix this up by just
removing the const pointer attribute as this is modified in numerous
places.

Link: https://lore.kernel.org/r/2025052145-undress-puma-f7cf@gregkh
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

drivers/usb/gadget/function/f_mass_storage.h

···
 };
 
 static inline struct fsg_opts *
-fsg_opts_from_func_inst(const struct usb_function_instance *fi)
+fsg_opts_from_func_inst(struct usb_function_instance *fi)
 {
 	return container_of(fi, struct fsg_opts, func_inst);
 }

include/linux/usb/composite.h

···
 	/* internals */
 	struct list_head		list;
 	DECLARE_BITMAP(endpoints, 32);
-	const struct usb_function_instance *fi;
+	struct usb_function_instance *fi;
 
 	unsigned int		bind_deactivated:1;
 };