drm/gma500: fix error path in gma_intel_setup_gmbus()

The current code fails to call i2c_del_adapter on
dev_prev->gmbus[0].adapter, and if the for loop above failed already
at i==0, all hell breaks loose when we do the loop body for
i = -1,-2,...

Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Link: http://patchwork.freedesktop.org/patch/msgid/1455048677-19882-2-git-send-email-linux@rasmusvillemoes.dk
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/gma500/intel_gmbus.c

@@ -436,7 +436,7 @@ int gma_intel_setup_gmbus(struct drm_device *dev)
 	return 0;
 
 err:
-	while (--i) {
+	while (i--) {
 		struct intel_gmbus *bus = &dev_priv->gmbus[i];
 		i2c_del_adapter(&bus->adapter);
 	}