drm/vkms: Use drm_crtc_vblank_crtc()

Replace the open coded drm_crtc_vblank_crtc() with the real
thing.

Cc: Rodrigo Siqueira <rodrigosiqueiramelo@gmail.com>
Cc: Melissa Wen <melissa.srw@gmail.com>
Cc: "Maíra Canal" <mairacanal@riseup.net>
Cc: Haneen Mohammed <hamohammed.sa@gmail.com>
Cc: Daniel Vetter <daniel@ffwll.ch>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240408190611.24914-5-ville.syrjala@linux.intel.comReviewed-by: Maíra Canal <mcanal@igalia.com>

drivers/gpu/drm/vkms/vkms_crtc.c

@@ -61,9 +61,7 @@ static enum hrtimer_restart vkms_vblank_simulate(struct hrtimer *timer)
 
 static int vkms_enable_vblank(struct drm_crtc *crtc)
 {
-	struct drm_device *dev = crtc->dev;
-	unsigned int pipe = drm_crtc_index(crtc);
-	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
+	struct drm_vblank_crtc *vblank = drm_crtc_vblank_crtc(crtc);
 	struct vkms_output *out = drm_crtc_to_vkms_output(crtc);
 
 	drm_calc_timestamping_constants(crtc, &crtc->mode);
@@ -88,10 +86,9 @@ static bool vkms_get_vblank_timestamp(struct drm_crtc *crtc,
 				      bool in_vblank_irq)
 {
 	struct drm_device *dev = crtc->dev;
-	unsigned int pipe = crtc->index;
 	struct vkms_device *vkmsdev = drm_device_to_vkms_device(dev);
 	struct vkms_output *output = &vkmsdev->output;
-	struct drm_vblank_crtc *vblank = &dev->vblank[pipe];
+	struct drm_vblank_crtc *vblank = drm_crtc_vblank_crtc(crtc);
 
 	if (!READ_ONCE(vblank->enabled)) {
 		*vblank_time = ktime_get();