Samples: fix a "value is always 0" Clang warning in xusb.c

* Remove the use of os_fd[i].recipient and alter comments with
  regards to Windows Extended Props test limitations with WinUSB

examples/xusb.c

diff --git a/examples/xusb.c b/examples/xusb.c
index b94aa1f..f1682ad 100644
--- a/examples/xusb.c
+++ b/examples/xusb.c
@@ -541,12 +541,7 @@
 		uint16_t header_size;
 	} os_fd[2] = {
 		{"Extended Compat ID", LIBUSB_RECIPIENT_DEVICE, 0x0004, 0x10},
-		{"Extended Properties", LIBUSB_RECIPIENT_DEVICE, 0x0005, 0x0A}
-		// NB: LIBUSB_RECIPIENT_INTERFACE should be used for the Extended Properties.
-		// However, for Interface requests, the WinUSB DLL forces the low byte of wIndex
-		// to the interface number, regardless of what you set it to, so we have to
-		// fallback to Device and hope the firmware answers both equally.
-		// See http://www.lvr.com/forum/index.php?topic=331
+		{"Extended Properties", LIBUSB_RECIPIENT_INTERFACE, 0x0005, 0x0A}
 	};
 
 	if (iface_number < 0) return;
@@ -555,7 +550,13 @@
 		printf("\nReading %s OS Feature Descriptor (wIndex = 0x%04d):\n", os_fd[i].desc, os_fd[i].index);
 
 		// Read the header part
-		r = libusb_control_transfer(handle, (uint8_t)(LIBUSB_ENDPOINT_IN|LIBUSB_REQUEST_TYPE_VENDOR|os_fd[i].recipient),
+		r = libusb_control_transfer(handle, (uint8_t)(LIBUSB_ENDPOINT_IN|LIBUSB_REQUEST_TYPE_VENDOR|LIBUSB_RECIPIENT_DEVICE),
+			// NB: We should use os_fd[i].recipient instead of LIBUSB_RECIPIENT_DEVICE above, as 
+			// LIBUSB_RECIPIENT_INTERFACE should be used for the Extended Properties.
+			// However, for Interface requests, the WinUSB DLL forces the low byte of wIndex
+			// to the interface number, regardless of what you set it to, so we have to
+			// fallback to Device and hope the firmware answers both equally.
+			// See http://www.lvr.com/forum/index.php?topic=331
 			bRequest, (uint16_t)(((iface_number)<< 8)|0x00), os_fd[i].index, os_desc, os_fd[i].header_size, 1000);
 		if (r < os_fd[i].header_size) {
 			perr("   Failed: %s", (r<0)?libusb_error_name((enum libusb_error)r):"header size is too small");