drm/i915: get runtime PM reference around GEM set_tiling IOCTL

After fixing the same issue in the set_caching IOCTL and Chris' request
to check out the possibilities for an improved RPM ref handling I
noticed that we have the same issue in the set_tiling IOCTL. Fix this
up.I didn't see any bug reports about this one, but the GTT unbind
operation on this path accesses the HW, which needs the ref.

Signed-off-by: Imre Deak <imre.deak@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1447092986-11165-1-git-send-email-imre.deak@intel.com

drivers/gpu/drm/i915/i915_gem_tiling.c

@@ -176,6 +176,8 @@ i915_gem_set_tiling(struct drm_device *dev, void *data,
 		return -EINVAL;
 	}
 
+	intel_runtime_pm_get(dev_priv);
+
 	mutex_lock(&dev->struct_mutex);
 	if (obj->pin_display || obj->framebuffer_references) {
 		ret = -EBUSY;
@@ -269,6 +271,8 @@ err:
 	drm_gem_object_unreference(&obj->base);
 	mutex_unlock(&dev->struct_mutex);
 
+	intel_runtime_pm_put(dev_priv);
+
 	return ret;
 }