iio: trigger: stm32-timer: Convert sysfs sprintf/snprintf family to sysfs_emit

Fix the following coccicheck warning:
drivers/iio/trigger/stm32-timer-trigger.c:299:8-16: WARNING:
use scnprintf or sprintf
Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Link: https://lore.kernel.org/r/1618216751-1678-4-git-send-email-tiantao6@hisilicon.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/trigger/stm32-timer-trigger.c

@@ -296,7 +296,7 @@ static ssize_t stm32_tt_show_master_mode(struct device *dev,
 	else
 		cr2 = (cr2 & TIM_CR2_MMS) >> TIM_CR2_MMS_SHIFT;
 
-	return snprintf(buf, PAGE_SIZE, "%s\n", master_mode_table[cr2]);
+	return sysfs_emit(buf, "%s\n", master_mode_table[cr2]);
 }
 
 static ssize_t stm32_tt_store_master_mode(struct device *dev,