pwm: spear: fix check on pwmchip_add() return value

pwmchip_add() returns zero on success and a negative value on error,
so the condition of the check must be inverted.

Signed-off-by: Beniamino Galvani <b.galvani@gmail.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Thierry Reding <thierry.reding@gmail.com>

drivers/pwm/pwm-spear.c

@@ -220,7 +220,7 @@ static int spear_pwm_probe(struct platform_device *pdev)
 	}
 
 	ret = pwmchip_add(&pc->chip);
-	if (!ret) {
+	if (ret < 0) {
 		clk_unprepare(pc->clk);
 		dev_err(&pdev->dev, "pwmchip_add() failed: %d\n", ret);
 	}