regulator: qcom-rpm: signedness bug in probe()

"force_mode" is a u32 so it is never "< 0", but because of type
promotion then comparing "== -1" will do what we want.
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/regulator/qcom_rpm-regulator.c

@@ -768,7 +768,7 @@ static int rpm_reg_probe(struct platform_device *pdev)
 			break;
 		}
 
-		if (force_mode < 0) {
+		if (force_mode == -1) {
 			dev_err(&pdev->dev, "invalid force mode\n");
 			return -EINVAL;
 		}