hwmon: (jz4740) fix signedness bug

wait_for_completion_interruptible_timeout() may return negative value.
In this case, checking if (t > 0)  will return true if t is unsigned.
Signed-off-by: Axel Lin <axel.lin@gmail.com>
Acked-by: Lars-Peter Clausen <lars@metafoo.de>
Cc: stable@kernel.org (3.0+)
Signed-off-by: Guenter Roeck <guenter.roeck@ericsson.com>

drivers/hwmon/jz4740-hwmon.c

@@ -59,7 +59,7 @@ static ssize_t jz4740_hwmon_read_adcin(struct device *dev,
 {
 	struct jz4740_hwmon *hwmon = dev_get_drvdata(dev);
 	struct completion *completion = &hwmon->read_completion;
-	unsigned long t;
+	long t;
 	unsigned long val;
 	int ret;