drm/omap: handle error if scale coefs are not found

If get_scale_coef functions fail, they return NULL, but we never check
the return value and could do a NULL deref. This should not happen as we
ought to validate the amount of scaling already earlier, but to be safe,
add the necessary check.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180502091159.7071-3-tomi.valkeinen@ti.com
Reviewed-by: Benoit Parrot <bparrot@ti.com>
Reviewed-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>

drivers/gpu/drm/omapdrm/dss/dispc.c

@@ -828,6 +828,12 @@ static void dispc_ovl_set_scale_coef(struct dispc_device *dispc,
 	h_coef = dispc_ovl_get_scale_coef(fir_hinc, true);
 	v_coef = dispc_ovl_get_scale_coef(fir_vinc, five_taps);
 
+	if (!h_coef || !v_coef) {
+		dev_err(&dispc->pdev->dev, "%s: failed to find scale coefs\n",
+			__func__);
+		return;
+	}
+
 	for (i = 0; i < 8; i++) {
 		u32 h, hv;