build: Don't depend on sdbusplus.found()

We can't depend on this for determining if we are using sdbusplus from a
subproject or not. If the project including phosphor-dbus-interfaces
finds the sdbusplus dependency first, this will show as found and use
the wrong routine for finding the tools.

Change-Id: Id1870ecc5a330cc26ea242657255ebfe13fd0448
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/meson.build b/meson.build
index 6dec01e..74c088a 100644
--- a/meson.build
+++ b/meson.build
@@ -12,7 +12,7 @@
 
 # Get sdbusplus dependency.
 sdbusplus_dep = dependency('sdbusplus', required: false)
-if sdbusplus_dep.found()
+if sdbusplus_dep.found() and sdbusplus_dep.type_name() != 'internal'
     sdbusplusplus_prog = find_program('sdbus++', native: true)
     sdbuspp_gen_meson_prog = find_program('sdbus++-gen-meson', native: true)
 else