usb: gadget: f_dfu.c: fix memory leak

dfu_prepare_function() allocates N+1 descriptor header structures,
the last one being the "DFU Functional Descriptor".

dfu_unbind() handles de-allocation, but fails to free the final
one (eg. "DFU Functional Descriptor"), leading to memory leak.

Fixed by incrementing counter, as in dfu_prepare_function().

Signed-off-by: Ralph Siemsen <ralph.siemsen@linaro.org>

drivers/usb/gadget/f_dfu.c

@@ -748,6 +748,7 @@ static void dfu_unbind(struct usb_configuration *c, struct usb_function *f)
 
 	if (f_dfu->function) {
 		i = alt_num;
+		i++; /* free DFU Functional Descriptor */
 		while (i) {
 			free(f_dfu->function[--i]);
 			f_dfu->function[i] = NULL;