gspca: Fix falling back to lower isoc alt settings

The current gspca core code has a regression where it no longer properly
falls back to lower alt settings when there is not enough bandwidth.

This causes many iso based usb-1 cameras to not work when plugged into a
usb2 hub or a sandybridge chipset motherboard!

This patch fixes this.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

drivers/media/video/gspca/gspca.c

@@ -957,7 +957,7 @@ retry:
 				ret = -EIO;
 				goto out;
 			}
-			alt = ep_tb[--alt_idx].alt;
+			gspca_dev->alt = ep_tb[--alt_idx].alt;
 		}
 	}
 out: