drm/i915: Remove modeset lock check from intel_pipe_update_start()

A follow up patch will call this funcion from a work context for the
mmio flip, in which case we cannot acquire the modeset locks. That's
not a problem though, since the check is there to protect vblank and
the mode, but the code that changes that waits for pending flips
first.
Signed-off-by: NAnder Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_sprite.c

@@ -86,8 +86,6 @@ static bool intel_pipe_update_start(struct intel_crtc *crtc, uint32_t *start_vbl
 	wait_queue_head_t *wq = drm_crtc_vblank_waitqueue(&crtc->base);
 	DEFINE_WAIT(wait);
 
-	WARN_ON(!drm_modeset_is_locked(&crtc->base.mutex));
-
 	vblank_start = mode->crtc_vblank_start;
 	if (mode->flags & DRM_MODE_FLAG_INTERLACE)
 		vblank_start = DIV_ROUND_UP(vblank_start, 2);