drm/tegra: Fix a possible null pointer dereference

In tegra_crtc_reset(), new memory is allocated with kzalloc(), but
no check is performed. Before calling __drm_atomic_helper_crtc_reset,
state should be checked to prevent possible null pointer dereference.

Fixes: b7e0b04 ("drm/tegra: Convert to using __drm_atomic_helper_crtc_reset() for reset.")
Cc: stable@vger.kernel.org
Signed-off-by: Qiu-ji Chen <chenqiuji666@gmail.com>
Signed-off-by: Thierry Reding <treding@nvidia.com>
Link: https://lore.kernel.org/r/20241106095906.15247-1-chenqiuji666@gmail.com

Author: TomRita999

drivers/gpu/drm/tegra/dc.c

@@ -1393,7 +1393,10 @@ static void tegra_crtc_reset(struct drm_crtc *crtc)
 	if (crtc->state)
 		tegra_crtc_atomic_destroy_state(crtc, crtc->state);
 
-	__drm_atomic_helper_crtc_reset(crtc, &state->base);
+	if (state)
+		__drm_atomic_helper_crtc_reset(crtc, &state->base);
+	else
+		__drm_atomic_helper_crtc_reset(crtc, NULL);
 }
 
 static struct drm_crtc_state *