drm/vmwgfx: Use __drm_atomic_helper_crtc_reset

Now also comes with the added benefit of doing a drm_crtc_vblank_off(),
which means vblank state isn't ill-defined and fail-y at driver load
before the first modeset on each crtc.

v2: Compile fix. Oops.

Reviewed-by: Roland Scheidegger <[e-mail]>
Signed-off-by: Daniel Vetter <[e-mail]>
Cc: VMware Graphics <[e-mail]>
Cc: Roland Scheidegger <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]

drivers/gpu/drm/vmwgfx/vmwgfx_kms.c

···
 		return;
 	}
 
-	crtc->state = &vcs->base;
-	crtc->state->crtc = crtc;
+	__drm_atomic_helper_crtc_reset(crtc, &vcs->base);
 }