usb: Make portspeed return a read-only string

Current code is plain wrong, and there's no need to have a mutable string,
so fix function type and remove the intermediate variable.

Signed-off-by: Ismael Luceno <ismael.luceno@silicon-gears.com>

cmd/usb.c

@@ -316,26 +316,18 @@ static struct usb_device *usb_find_device(int devnum)
 	return NULL;
 }
 
-static inline char *portspeed(int speed)
+static inline const char *portspeed(int speed)
 {
-	char *speed_str;
-
 	switch (speed) {
 	case USB_SPEED_SUPER:
-		speed_str = "5 Gb/s";
+		return "5 Gb/s";
-		break;
 	case USB_SPEED_HIGH:
-		speed_str = "480 Mb/s";
+		return "480 Mb/s";
-		break;
 	case USB_SPEED_LOW:
-		speed_str = "1.5 Mb/s";
+		return "1.5 Mb/s";
-		break;
 	default:
-		speed_str = "12 Mb/s";
+		return "12 Mb/s";
-		break;
 	}
-
-	return speed_str;
 }
 
 /* shows the device tree recursively */

common/usb_hub.c

@@ -233,26 +233,18 @@ static struct usb_hub_device *usb_hub_allocate(void)
 
 #define MAX_TRIES 5
 
-static inline char *portspeed(int portstatus)
+static inline const char *portspeed(int portstatus)
 {
-	char *speed_str;
-
 	switch (portstatus & USB_PORT_STAT_SPEED_MASK) {
 	case USB_PORT_STAT_SUPER_SPEED:
-		speed_str = "5 Gb/s";
+		return "5 Gb/s";
-		break;
 	case USB_PORT_STAT_HIGH_SPEED:
-		speed_str = "480 Mb/s";
+		return "480 Mb/s";
-		break;
 	case USB_PORT_STAT_LOW_SPEED:
-		speed_str = "1.5 Mb/s";
+		return "1.5 Mb/s";
-		break;
 	default:
-		speed_str = "12 Mb/s";
+		return "12 Mb/s";
-		break;
 	}
-
-	return speed_str;
 }
 
 /**