mfd: ab8500-debugfs: Cleaning up unnecessary to test, unsigned can't be negative.

Unsigned variable can't be negative so it is unnecessary to test it

This was found using a static code analysis program called cppcheck
Signed-off-by: Rickard Strandqvist <rickard_strandqvist@spectrumdigital.se>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/ab8500-debugfs.c

@@ -2503,7 +2503,7 @@ static ssize_t ab8500_gpadc_trig_timer_write(struct file *file,
 	if (err)
 		return err;
 
-	if ((user_trig_timer >= 0) && (user_trig_timer <= 255)) {
+	if (user_trig_timer <= 255) {
 		trig_timer = (u8) user_trig_timer;
 	} else {
 		dev_err(dev, "debugfs error input: "