hwrng: core - convert sysfs sprintf/snprintf family to sysfs_emit

Fix the following coccicheck warning:

drivers/char/hw_random/core.c:399:8-16: WARNING: use scnprintf or sprintf.
Signed-off-by: Zihao Tang <tangzihao1@hisilicon.com>
Signed-off-by: Jay Fang <f.fangjian@huawei.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>

drivers/char/hw_random/core.c

@@ -396,7 +396,7 @@ static ssize_t hwrng_attr_selected_show(struct device *dev,
 					struct device_attribute *attr,
 					char *buf)
 {
-	return snprintf(buf, PAGE_SIZE, "%d\n", cur_rng_set_by_user);
+	return sysfs_emit(buf, "%d\n", cur_rng_set_by_user);
 }
 
 static DEVICE_ATTR(rng_current, S_IRUGO | S_IWUSR,