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: Ifef98dc70a24f41df1b199fcbf28fe034a5526bc
diff --git a/src/meson.build b/src/meson.build
index 939574e..411f0d4 100644
--- a/src/meson.build
+++ b/src/meson.build
@@ -12,7 +12,7 @@
     cpp_args: cpp_args + ['-DBOOST_ASIO_DISABLE_THREADS'],
     dependencies: [
         boost,
-        nlohmann_json,
+        nlohmann_json_dep,
         sdbusplus,
         valijson,
     ],
@@ -36,7 +36,7 @@
         dependencies: [
             boost,
             i2c,
-            nlohmann_json,
+            nlohmann_json_dep,
             sdbusplus,
             threads,
             valijson,