drm: Fix drm_crtc_vblank_get() documentation

drm_crtc_vblank_get() is the new drm_vblank_get(), not the new
drm_vblank_off().

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>
diff --git a/drivers/gpu/drm/drm_irq.c b/drivers/gpu/drm/drm_irq.c
index 10574a0..c9f5453 100644
--- a/drivers/gpu/drm/drm_irq.c
+++ b/drivers/gpu/drm/drm_irq.c
@@ -1052,7 +1052,7 @@
  * Acquire a reference count on vblank events to avoid having them disabled
  * while in use.
  *
- * This is the native kms version of drm_vblank_off().
+ * This is the native kms version of drm_vblank_get().
  *
  * Returns:
  * Zero on success, nonzero on failure.