USB: ti_usb_3410_5052: fix big-endian firmware handling

Fix endianess bugs in firmware handling introduced by commits cb7a7c6a
("ti_usb_3410_5052: add Multi-Tech modem support") and 05a3d905
("ti_usb_3410_5052: support alternate firmware") which made the driver
use the wrong firmware for certain devices on big-endian machines.

Cc: stable@vger.kernel.org
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>