spi: sprd: Fix the possible negative value of BIT()

When enabling the ADI hardware channels, if the channel id is 31,
then we will get one negative value -1 for BIT() macro, which will
write incorrect value to register.

Fixes: 7e2903cb91df ("spi: Add ADI driver for Spreadtrum platform")
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Baolin Wang <baolin.wang@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-sprd-adi.c

@@ -303,7 +303,7 @@ static void sprd_adi_hw_init(struct sprd_adi *sadi)
 		writel_relaxed(chn_config, sadi->base +
 			       REG_ADI_CHN_ADDR(chn_id));
 
-		if (chn_id < 31) {
+		if (chn_id < 32) {
 			value = readl_relaxed(sadi->base + REG_ADI_CHN_EN);
 			value |= BIT(chn_id);
 			writel_relaxed(value, sadi->base + REG_ADI_CHN_EN);