fix(drivers/usb): remove unnecessary cast

Remove the unnecessary cast on the result of function which
already return the correct type.

Signed-off-by: Patrick Delaunay <patrick.delaunay@foss.st.com>
Change-Id: Ie21f7e78a880d30d1f31e32b3d2c3fb09489d65b
diff --git a/drivers/usb/usb_device.c b/drivers/usb/usb_device.c
index ce02d4f..7fcb39b 100644
--- a/drivers/usb/usb_device.c
+++ b/drivers/usb/usb_device.c
@@ -73,7 +73,7 @@
 		break;
 
 	case USB_DESC_TYPE_CONFIGURATION:
-		pbuf = (uint8_t *)pdev->desc->get_config_desc(&len);
+		pbuf = pdev->desc->get_config_desc(&len);
 		pbuf[1] = USB_DESC_TYPE_CONFIGURATION;
 		break;
 
@@ -112,11 +112,11 @@
 		break;
 
 	case USB_DESC_TYPE_DEVICE_QUALIFIER:
-		pbuf = (uint8_t *)pdev->desc->get_device_qualifier_desc(&len);
+		pbuf = pdev->desc->get_device_qualifier_desc(&len);
 		break;
 
 	case USB_DESC_TYPE_OTHER_SPEED_CONFIGURATION:
-		pbuf = (uint8_t *)pdev->desc->get_config_desc(&len);
+		pbuf = pdev->desc->get_config_desc(&len);
 		pbuf[1] = USB_DESC_TYPE_OTHER_SPEED_CONFIGURATION;
 		break;