drm/vblank: Fix documentation of VBLANK timestamp helper

Per-CRTC VBLANK information used to be addressed by device and pipe
index. A call drm_crtc_vblank_helper_get_vblank_timestamp_internal()
receives a pointer to the CRTC instead. Fix the documentation.
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reported-by: Daniel Vetter <daniel@ffwll.ch>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Fixes: f1e2b637 ("drm: Add get_scanout_position() to struct drm_crtc_helper_funcs")
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Maxime Ripard <mripard@kernel.org>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: dri-devel@lists.freedesktop.org
Link: https://patchwork.freedesktop.org/patch/msgid/20200303073135.10605-1-tzimmermann@suse.de

drivers/gpu/drm/drm_vblank.c

@@ -592,8 +592,7 @@ EXPORT_SYMBOL(drm_calc_timestamping_constants);
 /**
  * drm_crtc_vblank_helper_get_vblank_timestamp_internal - precise vblank
  *                                                        timestamp helper
- * @dev: DRM device
- * @pipe: index of CRTC whose vblank timestamp to retrieve
+ * @crtc: CRTC whose vblank timestamp to retrieve
  * @max_error: Desired maximum allowable error in timestamps (nanosecs)
  *             On return contains true maximum error of timestamp
  * @vblank_time: Pointer to time which should receive the timestamp