drm/mediatek: dp: Add missing error checks in mtk_dp_parse_capabilities

If reading the RX capabilities fails the training pattern will be set
wrongly: add error checking for drm_dp_read_dpcd_caps() and return if
anything went wrong with it.

While at it, also add a less critical error check when writing to
clear the ESI0 IRQ vector.

Fixes: f70ac097 ("drm/mediatek: Add MT8195 Embedded DisplayPort driver")
Signed-off-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Tested-by: Chen-Yu Tsai <wenst@chromium.org>
Reviewed-by: Alexandre Mergnat <amergnat@baylibre.com>
Reviewed-by: CK Hu <ck.hu@mediatek.com>
Link: https://patchwork.kernel.org/project/dri-devel/patch/20230725073234.55892-2-angelogioacchino.delregno@collabora.com/Signed-off-by: Chun-Kuang Hu <chunkuang.hu@kernel.org>

drivers/gpu/drm/mediatek/mtk_dp.c

@@ -1588,7 +1588,9 @@ static int mtk_dp_parse_capabilities(struct mtk_dp *mtk_dp)
 	u8 val;
 	ssize_t ret;
 
-	drm_dp_read_dpcd_caps(&mtk_dp->aux, mtk_dp->rx_cap);
+	ret = drm_dp_read_dpcd_caps(&mtk_dp->aux, mtk_dp->rx_cap);
+	if (ret < 0)
+		return ret;
 
 	if (drm_dp_tps4_supported(mtk_dp->rx_cap))
 		mtk_dp->train_info.channel_eq_pattern = DP_TRAINING_PATTERN_4;
@@ -1615,10 +1617,13 @@ static int mtk_dp_parse_capabilities(struct mtk_dp *mtk_dp)
 			return ret == 0 ? -EIO : ret;
 		}
 
-		if (val)
-			drm_dp_dpcd_writeb(&mtk_dp->aux,
+		if (val) {
+			ret = drm_dp_dpcd_writeb(&mtk_dp->aux,
 						 DP_DEVICE_SERVICE_IRQ_VECTOR_ESI0,
 						 val);
+			if (ret < 0)
+				return ret;
+		}
 	}
 
 	return 0;