Merge pull request #14970 from MubeenHCLite/USBSerial_connect_blocking_resolution

USB connect problem in non blocking mode

Author: 0xc0170

targets/TARGET_STM/USBPhy_STM32.cpp

@@ -318,6 +318,7 @@ void USBPhyHw::init(USBPhyEvents *events)
     HAL_StatusTypeDef ret = HAL_PCD_Init(&hpcd);
     MBED_ASSERT(ret == HAL_OK);
     __HAL_PCD_ENABLE(&hpcd);
+    HAL_PCD_Start(&hpcd);
 
     // Configure FIFOs
 #if (MBED_CONF_TARGET_USB_SPEED == USE_USB_NO_OTG)