pinctrl: stmfx: Remove duplicated code

In stmfx_read_reg there is duplicated code to detect ret < 0 and return
ret if so. Remove one version of it.

This issue was found by Smatch.

Signed-off-by: Andrew Goodbody <andrew.goodbody@linaro.org>

drivers/pinctrl/pinctrl-stmfx.c

@@ -87,7 +87,7 @@ static int stmfx_read_reg(struct udevice *dev, u8 reg_base, uint offset)
 	if (ret < 0)
 		return ret;
 
-	return ret < 0 ? ret : !!(ret & mask);
+	return !!(ret & mask);
 }
 
 static int stmfx_write_reg(struct udevice *dev, u8 reg_base, uint offset,