drm/i915: Remove the error message for unbinding pinned buffers

This is now used intentionally to prevent proliferation of is-pinned
checks upon the inactive list following:

commit 1b50247a8ddde4af5aaa0e6bc125615372ce6c16
Author: Chris Wilson <chris@chris-wilson.co.uk>
Date:   Tue Apr 24 15:47:30 2012 +0100

    drm/i915: Remove the list of pinned inactive objects

Reported-and-tested-by: guang.a.yang@intel.com
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=50075
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem.c

@@ -2033,10 +2033,8 @@ i915_gem_object_unbind(struct drm_i915_gem_object *obj)
 	if (obj->gtt_space == NULL)
 		return 0;
 
-	if (obj->pin_count != 0) {
-		DRM_ERROR("Attempting to unbind pinned buffer\n");
-		return -EINVAL;
-	}
+	if (obj->pin_count)
+		return -EBUSY;
 
 	ret = i915_gem_object_finish_gpu(obj);
 	if (ret)