Fix QA license warning

[Paullgk]

Currently, libflann and pcl recipes, both under BSD license dot not specify the BSD license version. As results, this causes QA warnings, such as:

WARNING: image-1.0-r0 do_rootfs: QA Issue: The license listed BSD was not in the licenses collected for recipe pcl [license-file-missing]
WARNING: libflann-1.9.1-r0 do_populate_lic: QA Issue: libflann: No generic license file exists for: BSD in any provider [license-exists]

This can be fixed by specifying the good license version, here BSD-3 for both recipes.