[PATCH] 4.15 vmgfx boot warning

[Woody Suwalski]

The 4.15 vmwgfx driver shows a warning during boot (32 bit x86)
It is caused by a mismatch between the result of vmw_enable_vblank() and 
what the drm_atomic_helper expects:
    /...
    ret = drm_crtc_vblank_get(crtc);
    WARN_ONCE(ret != -EINVAL, "driver forgot to call 
drm_crtc_vblank_off()\n");
    /...

Signed-off by: Woody Suwalski <terraluna977 at gmail.com>

--- a/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c    2017-11-22 
15:29:46.511674079 -0500
+++ b/drivers/gpu/drm/vmwgfx/vmwgfx_kms.c    2017-11-22 
15:30:35.344559592 -0500
@@ -1869,7 +1869,7 @@ u32 vmw_get_vblank_counter(struct drm_de
   */
  int vmw_enable_vblank(struct drm_device *dev, unsigned int pipe)
  {
-    return -ENOSYS;
+    return -EINVAL;
  }

  /**