build: fix missing nlohmann_json dependency

Subproject builds are currently broken due to a missing dependency
in the `topology` unit-tests.

Signed-off-by: Patrick Williams <patrick@stwcx.xyz>
Change-Id: Id516d790fa48fd2e49db65d97abe3b21ae305f86
diff --git a/meson.build b/meson.build
index 2c473a2..4b01613 100644
--- a/meson.build
+++ b/meson.build
@@ -260,6 +260,7 @@
             dependencies: [
                 gtest,
                 gmock,
+                nlohmann_json_dep,
             ],
             include_directories: 'src',
         )