libusb: Adapt to FreeBSD 10

FreeBSD 10 has libusb_get_string_descriptor() in base libusb, so don't
define it here.

Author: blabber

libusb/hid.c

@@ -313,9 +313,9 @@ static int get_usage(uint8_t *report_descriptor, size_t size,
 }
 #endif /* INVASIVE_GET_USAGE */
 
-#ifdef __FreeBSD__
-/* The FreeBSD version of libusb doesn't have this funciton. In mainline
-   libusb, it's inlined in libusb.h. This function will bear a striking
+#if defined(__FreeBSD__) && __FreeBSD__ < 10
+/* The libusb version included in FreeBSD < 10 doesn't have this function. In
+   mainline libusb, it's inlined in libusb.h. This function will bear a striking
    resemblence to that one, because there's about one way to code it.
 
    Note that the data parameter is Unicode in UTF-16LE encoding.