meson: nlohmann/json has a meson build

Exploit the usual configuration available for subprojects that support
meson directly.

Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
Change-Id: I410cc14ca426b1c4c26600f6a72a47aa4d944570
diff --git a/src/meson.build b/src/meson.build
index 8a9811b..1a445b3 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -8,7 +8,7 @@
     cpp_args: cpp_args + ['-DBOOST_ASIO_DISABLE_THREADS'],
     dependencies: [
         boost,
-        nlohmann_json,
+        nlohmann_json_dep,
         sdbusplus,
         valijson,
     ],
@@ -31,7 +31,7 @@
         dependencies: [
             boost,
             i2c,
-            nlohmann_json,
+            nlohmann_json_dep,
             sdbusplus,
             threads,
             valijson,