libftdi: Fix compilation with most recent CMake

libftdi: Fix compilation with most recent CMake

Description from Amol Bhave:

This package fails to compile with boost 1.70 when the boost cmake
config gets used.
As far as I can tell, Boost 1.70 introduced
BoostConfigVersion.cmake. In that file, the value of PACKAGE_VERSION is
set to 1.70. This makes CMake auto set the variable Boost_VERSION to
1.70. Historically, Boost_VERSION has been using the format like 170000,
and not 1.70. Some package cmake files still depend on this behavior
and make assertions such as Boost_VERSION > 168000. This is incompatible
with the new scheme.

Signed-off-by: Rosen Penev <rosenp@gmail.com>