iio: adc: stmpe-adc: Fix wait_for_completion_timeout return value check

wait_for_completion_timeout() returns unsigned long not long.
it returns 0 if timed out, and positive if completed.
The check for <= 0 is ambiguous and should be == 0 here
indicating timeout which is the only error case

Fixes: e813dde6 ("iio: stmpe-adc: Use wait_for_completion_timeout")
Signed-off-by: Miaoqian Lin <linmq006@gmail.com>
Reviewed-by: Philippe Schenker <philippe.schenker@toradex.com>
Link: https://lore.kernel.org/r/20220412065150.14486-1-linmq006@gmail.comSigned-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

drivers/iio/adc/stmpe-adc.c

@@ -61,7 +61,7 @@ struct stmpe_adc {
 static int stmpe_read_voltage(struct stmpe_adc *info,
 		struct iio_chan_spec const *chan, int *val)
 {
-	long ret;
+	unsigned long ret;
 
 	mutex_lock(&info->lock);
 
@@ -79,7 +79,7 @@ static int stmpe_read_voltage(struct stmpe_adc *info,
 
 	ret = wait_for_completion_timeout(&info->completion, STMPE_ADC_TIMEOUT);
 
-	if (ret <= 0) {
+	if (ret == 0) {
 		stmpe_reg_write(info->stmpe, STMPE_REG_ADC_INT_STA,
 				STMPE_ADC_CH(info->channel));
 		mutex_unlock(&info->lock);
@@ -96,7 +96,7 @@ static int stmpe_read_voltage(struct stmpe_adc *info,
 static int stmpe_read_temp(struct stmpe_adc *info,
 		struct iio_chan_spec const *chan, int *val)
 {
-	long ret;
+	unsigned long ret;
 
 	mutex_lock(&info->lock);
 
@@ -114,7 +114,7 @@ static int stmpe_read_temp(struct stmpe_adc *info,
 
 	ret = wait_for_completion_timeout(&info->completion, STMPE_ADC_TIMEOUT);
 
-	if (ret <= 0) {
+	if (ret == 0) {
 		mutex_unlock(&info->lock);
 		return -ETIMEDOUT;
 	}