USB: mos7840: fix big-endian probe

Fix bug in device-type detection on big-endian machines originally
introduced by commit 0eafe4de

 ("USB: serial: mos7840: add support for
MCS7810 devices") which always matched on little-endian product ids.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Cc: stable@vger.kernel.org
Signed-off-by: Johan Hovold <jhovold@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>