usb: typec: stusb160x: fix signedness comparison issue with enum variables

chip->port_type and chip->pwr_opmode are enums and when GCC considers them
as unsigned, the conditions are never met.
This patch takes advantage of the ret variable and fixes the following
warnings:
drivers/usb/typec/stusb160x.c:548 stusb160x_get_fw_caps() warn: unsigned 'chip->port_type' is never less than zero.
drivers/usb/typec/stusb160x.c:570 stusb160x_get_fw_caps() warn: unsigned 'chip->pwr_opmode' is never less than zero.

Fixes: da0cb63 ("usb: typec: add support for STUSB160x Type-C controller family")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Amelie Delaunay <amelie.delaunay@st.com>
Link: https://lore.kernel.org/r/20201028163309.12878-1-amelie.delaunay@st.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Author: ADESTM

drivers/usb/typec/stusb160x.c

@@ -544,11 +544,10 @@ static int stusb160x_get_fw_caps(struct stusb160x *chip,
 	 */
 	ret = fwnode_property_read_string(fwnode, "power-role", &cap_str);
 	if (!ret) {
-		chip->port_type = typec_find_port_power_role(cap_str);
-		if ((int)chip->port_type < 0) {
-			ret = chip->port_type;
+		ret = typec_find_port_power_role(cap_str);
+		if (ret < 0)
 			return ret;
-		}
+		chip->port_type = ret;
 	}
 	chip->capability.type = chip->port_type;
 
@@ -565,16 +564,13 @@ static int stusb160x_get_fw_caps(struct stusb160x *chip,
 	 */
 	ret = fwnode_property_read_string(fwnode, "power-opmode", &cap_str);
 	if (!ret) {
-		chip->pwr_opmode = typec_find_pwr_opmode(cap_str);
+		ret = typec_find_pwr_opmode(cap_str);
 		/* Power delivery not yet supported */
-		if ((int)chip->pwr_opmode < 0 ||
-		    chip->pwr_opmode == TYPEC_PWR_MODE_PD) {
-			ret = (int)chip->pwr_opmode < 0 ? chip->pwr_opmode :
-							  -EINVAL;
-			dev_err(chip->dev, "bad power operation mode: %d\n",
-				chip->pwr_opmode);
-			return ret;
+		if (ret < 0 || ret == TYPEC_PWR_MODE_PD) {
+			dev_err(chip->dev, "bad power operation mode: %d\n", ret);
+			return -EINVAL;
 		}
+		chip->pwr_opmode = ret;
 	}
 
 	return 0;