build: fix dependency check for nlohmann/json

Fix the following error observed in Yocto bump:

    | Has header "nlomann/json.hpp" : NO
    |
    | ../git/meson.build:24:4: ERROR: Automatic wrap-based subproject downloading is disabled
    |

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: I71a052f11d7d50c58ff5b16d124c54b636888f96
1 file changed