usb:st usbfs-v2: fix disconnect polarity

Fixes issue #1482: Incorrect interpretation of disconnected parameter in st_usbfs_v2_disconnect

The `disconnected` parameter was interpreted incorrectly: When set to true it connected but should disconnect.

Reviewed-by: Karl Palsson <karlp@tweak.au>

lib/stm32/st_usbfs_v2.c

@@ -90,9 +90,9 @@ static void st_usbfs_v2_disconnect(usbd_device *usbd_dev, bool disconnected)
 	(void)usbd_dev;
 	uint16_t reg = GET_REG(USB_BCDR_REG);
 	if (disconnected) {
-		SET_REG(USB_BCDR_REG, reg | USB_BCDR_DPPU);
-	} else {
 		SET_REG(USB_BCDR_REG, reg & ~USB_BCDR_DPPU);
+	} else {
+		SET_REG(USB_BCDR_REG, reg | USB_BCDR_DPPU);
 	}
 }