drm/i915: remove superfluous i915_gem_object_free_mmap_offset call

This should already be handled by drm_gem_object_release, which is
called later on.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1467720019-31876-1-git-send-email-matthew.auld@intel.com

drivers/gpu/drm/i915/i915_gem.c

@@ -4901,7 +4901,6 @@ void i915_gem_free_object(struct drm_gem_object *gem_obj)
 	if (discard_backing_storage(obj))
 		obj->madv = I915_MADV_DONTNEED;
 	i915_gem_object_put_pages(obj);
-	i915_gem_object_free_mmap_offset(obj);
 
 	BUG_ON(obj->pages);