meson: Add dependency override for phosphor-dbus-interfaces

Resolves e.g. the following when phosphor-dbus-interfaces is specified
as a subproject:

```
$ meson setup build
...
phosphor-logging| WARNING: Subproject 'phosphor-dbus-interfaces' did not override 'phosphor-dbus-interfaces' dependency and no variable name specified
phosphor-logging| Dependency phosphor-dbus-interfaces from subproject subprojects/phosphor-dbus-interfaces found: NO

subprojects/phosphor-logging/meson.build:26:0: ERROR: Dependency 'phosphor-dbus-interfaces' is required but not found.
...
```

Change-Id: Ie549c377e71297e9748322be2f2e0c0153c104f7
Signed-off-by: Andrew Jeffery <andrew@aj.id.au>
diff --git a/meson.build b/meson.build
index 70cd52a..6a724de 100644
--- a/meson.build
+++ b/meson.build
@@ -145,3 +145,5 @@
     dependencies: sdbusplus_dep,
     variables: ['yamldir=' + meson.project_source_root() / 'yaml'],
 )
+
+meson.override_dependency('phosphor-dbus-interfaces', phosphor_dbus_interfaces_dep)