flann: Disable find package for HDF5

flann: Disable find package for HDF5

The HDF5 package is used by flann for testing purpose only and is
not part of buildroot packages. However, if present in the host, it will
be used and trigger the unsafe header/library path used in
cross-compilation error.

Signed-off-by: Johan Oudinet <johan.oudinet@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
(cherry picked from commit f6ee339e92360fc43ebe17928656c06634b09c97)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>