usb: dwc3: drop EP0_STALL state

Whenever we issue a Set Stall command on EP0,
the state machine will be restarted and Stall
is cleared automatically, when core receives
the next SETUP packet.

There's no need to track that EP0_STALL state.

Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/dwc3/ep0.c

@@ -68,8 +68,6 @@ static const char *dwc3_ep0_state_string(enum dwc3_ep0_state state)
 		return "Data Phase";
 	case EP0_STATUS_PHASE:
 		return "Status Phase";
-	case EP0_STALL:
-		return "Stall";
 	default:
 		return "UNKNOWN";
 	}