drm/i915: Early return for no-op i915_vma_pin_fence()

If we have no fence and desire no fence on the vma, return before we try
and take the vm->mutex.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200108153550.3803446-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_gem_fence_reg.c

@@ -412,6 +412,9 @@ int i915_vma_pin_fence(struct i915_vma *vma)
 {
 	int err;
 
+	if (!vma->fence && !i915_gem_object_is_tiled(vma->obj))
+		return 0;
+
 	/*
 	 * Note that we revoke fences on runtime suspend. Therefore the user
 	 * must keep the device awake whilst using the fence.