Windows: fix Clang warnings about unused assignations

libusb/os/threads_windows.c

diff --git a/libusb/os/threads_windows.c b/libusb/os/threads_windows.c
index 8a29920..fe2bfc1 100644
--- a/libusb/os/threads_windows.c
+++ b/libusb/os/threads_windows.c
@@ -99,7 +99,6 @@
 		prev_pos = pos;
 	}
 	free(prev_pos);
-	prev_pos = pos = NULL;
 
 	return 0;
 }

libusb/os/windows_usb.c

diff --git a/libusb/os/windows_usb.c b/libusb/os/windows_usb.c
index 0ae66e9..6552ed6 100644
--- a/libusb/os/windows_usb.c
+++ b/libusb/os/windows_usb.c
@@ -1183,7 +1183,7 @@
  */
 static int windows_get_device_list(struct libusb_context *ctx, struct discovered_devs **_discdevs)
 {
-	struct discovered_devs *discdevs = *_discdevs;
+	struct discovered_devs *discdevs;
 	HDEVINFO dev_info = { 0 };
 	char* usb_class[2] = {"USB", "NUSB3"};
 	SP_DEVINFO_DATA dev_info_data;
@@ -1262,7 +1262,6 @@
 			safe_free(dev_interface_details);
 			safe_free(dev_interface_path);
 			safe_free(dev_id_path);
-			session_id = 0;
 			priv = parent_priv = NULL;
 			dev = parent_dev = NULL;