net: irda: irda-usb: fix firmware name on big-endian hosts

Add missing endianness conversion when using the USB device-descriptor
bcdDevice field to construct a firmware file name.

Fixes: 8ef80aef ("[IRDA]: irda-usb.c: STIR421x cleanups")
Cc: stable <stable@vger.kernel.org>     # 2.6.18
Cc: Nick Fedchik <nfedchik@atlantic-link.com.ua>
Signed-off-by: Johan Hovold <johan@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>