drm/i915: fix error path in intel_setup_gmbus()

commit ed3f9fd1 upstream.

This fails to undo the setup for pin==0; moreover, something
interesting happens if the setup failed already at pin==0.
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Fixes: f899fc64 ("drm/i915: use GMBUS to manage i2c links")
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1455048677-19882-3-git-send-email-linux@rasmusvillemoes.dk
(cherry picked from commit 2417c8c0)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
[ luis: backported to 3.16:
  - use 'i' instead of 'pin'
  - adjusted context ]
Signed-off-by: Luis Henriques <luis.henriques@canonical.com>

drivers/gpu/drm/i915/intel_i2c.c

@@ -680,7 +680,7 @@ int 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);
 	}