drm: bridge: sii8620: fix possible off-by-one

The next call to sii8620_burst_get_tx_buf will result in off-by-one
When ctx->burst.tx_count + size == ARRAY_SIZE(ctx->burst.tx_buf). The same
thing happens in sii8620_burst_get_rx_buf.

This patch also change tx_count and tx_buf to rx_count and rx_buf in
sii8620_burst_get_rx_buf. It is unreasonable to check tx_buf's size and
use rx_buf.

Fixes: e19e9c69 ("drm/bridge/sii8620: add support for burst eMSC transmissions")
Signed-off-by: Hangyu Hua <hbh25y@gmail.com>
Reviewed-by: Andrzej Hajda <andrzej.hajda@intel.com>
Signed-off-by: Robert Foss <robert.foss@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20220518065856.18936-1-hbh25y@gmail.com

drivers/gpu/drm/bridge/sil-sii8620.c

@@ -605,7 +605,7 @@ static void *sii8620_burst_get_tx_buf(struct sii8620 *ctx, int len)
 	u8 *buf = &ctx->burst.tx_buf[ctx->burst.tx_count];
 	int size = len + 2;
 
-	if (ctx->burst.tx_count + size > ARRAY_SIZE(ctx->burst.tx_buf)) {
+	if (ctx->burst.tx_count + size >= ARRAY_SIZE(ctx->burst.tx_buf)) {
 		dev_err(ctx->dev, "TX-BLK buffer exhausted\n");
 		ctx->error = -EINVAL;
 		return NULL;
@@ -622,7 +622,7 @@ static u8 *sii8620_burst_get_rx_buf(struct sii8620 *ctx, int len)
 	u8 *buf = &ctx->burst.rx_buf[ctx->burst.rx_count];
 	int size = len + 1;
 
-	if (ctx->burst.tx_count + size > ARRAY_SIZE(ctx->burst.tx_buf)) {
+	if (ctx->burst.rx_count + size >= ARRAY_SIZE(ctx->burst.rx_buf)) {
 		dev_err(ctx->dev, "RX-BLK buffer exhausted\n");
 		ctx->error = -EINVAL;
 		return NULL;