media: si21xx: use time_is_before_jiffies() instead of open coding it

Use the helper function time_is_{before,after}_jiffies() to improve
code readability.
Signed-off-by: Wang Qing <wangqing@vivo.com>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>

drivers/media/dvb-frontends/si21xx.c

@@ -336,7 +336,7 @@ static int si21xx_wait_diseqc_idle(struct si21xx_state *state, int timeout)
 	dprintk("%s\n", __func__);
 
 	while ((si21_readreg(state, LNB_CTRL_REG_1) & 0x8) == 8) {
-		if (jiffies - start > timeout) {
+		if (time_is_before_jiffies(start + timeout)) {
 			dprintk("%s: timeout!!\n", __func__);
 			return -ETIMEDOUT;
 		}