ASoC: renesas: rz-ssi: Add a check for negative sample_space

My static checker rule complains about this code.  The concern is that
if "sample_space" is negative then the "sample_space >= runtime->channels"
condition will not work as intended because it will be type promoted to a
high unsigned int value.

strm->fifo_sample_size is SSI_FIFO_DEPTH (32).  The SSIFSR_TDC_MASK is
0x3f.  Without any further context it does seem like a reasonable warning
and it can't hurt to add a check for negatives.

Cc: stable@vger.kernel.org
Fixes: 03e786b ("ASoC: sh: Add RZ/G2L SSIF-2 driver")
Signed-off-by: Dan Carpenter <dan.carpenter@linaro.org>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://patch.msgid.link/e07c3dc5-d885-4b04-a742-71f42243f4fd@stanley.mountain
Signed-off-by: Mark Brown <broonie@kernel.org>

Author: Dan Carpenter

sound/soc/renesas/rz-ssi.c

@@ -521,6 +521,8 @@ static int rz_ssi_pio_send(struct rz_ssi_priv *ssi, struct rz_ssi_stream *strm)
 	sample_space = strm->fifo_sample_size;
 	ssifsr = rz_ssi_reg_readl(ssi, SSIFSR);
 	sample_space -= (ssifsr >> SSIFSR_TDC_SHIFT) & SSIFSR_TDC_MASK;
+	if (sample_space < 0)
+		return -EINVAL;
 
 	/* Only add full frames at a time */
 	while (frames_left && (sample_space >= runtime->channels)) {