usb: gadget: ffs: fix enable multiple instances

This patch fixes an "off-by-one" bug found in
581791f5 (FunctionFS: enable multiple functions).

During gfs_bind/gfs_unbind the functionfs_bind/functionfs_unbind should be
called for every functionfs instance. With the "i" pre-decremented they
were not called for the zeroth instance.
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>
Cc: <stable@vger.kernel.org>

[ balbi@ti.com : added offending commit's subject ]
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/g_ffs.c

@@ -357,7 +357,7 @@ static int gfs_bind(struct usb_composite_dev *cdev)
 		goto error;
 	gfs_dev_desc.iProduct = gfs_strings[USB_GADGET_PRODUCT_IDX].id;
 
-	for (i = func_num; --i; ) {
+	for (i = func_num; i--; ) {
 		ret = functionfs_bind(ffs_tab[i].ffs_data, cdev);
 		if (unlikely(ret < 0)) {
 			while (++i < func_num)
@@ -413,7 +413,7 @@ static int gfs_unbind(struct usb_composite_dev *cdev)
 		gether_cleanup();
 	gfs_ether_setup = false;
 
-	for (i = func_num; --i; )
+	for (i = func_num; i--; )
 		if (ffs_tab[i].ffs_data)
 			functionfs_unbind(ffs_tab[i].ffs_data);