drm/i915: Remove unused variable from i915_gem_mmap_gtt

Lost in

commit c5ad54cf
Author: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Date:   Wed May 6 14:36:09 2015 +0300

    drm/i915: Use partial view in mmap fault handler

Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>

drivers/gpu/drm/i915/i915_gem.c

@@ -1919,7 +1919,6 @@ i915_gem_mmap_gtt(struct drm_file *file,
 		  uint32_t handle,
 		  uint64_t *offset)
 {
-	struct drm_i915_private *dev_priv = dev->dev_private;
 	struct drm_i915_gem_object *obj;
 	int ret;