pw_protobuf_compiler: Fix dependency bug

This change fixes an issue in the proto build code where proto
dependencies were not being set for all generators.

Change-Id: Iaac38845480705c2f79d0d6280ff4e240e1feba7
diff --git a/pw_protobuf_compiler/proto.gni b/pw_protobuf_compiler/proto.gni
index 58306dc..4a26bdc 100644
--- a/pw_protobuf_compiler/proto.gni
+++ b/pw_protobuf_compiler/proto.gni
@@ -258,13 +258,12 @@
 
   foreach(_gen, pw_protobuf_generators) {
     _lang_target = "${target_name}_${_gen}"
+    _gen_deps = []
+    if (defined(invoker.deps)) {
+      _gen_deps = process_file_template(invoker.deps, "{{source}}_${_gen}")
+    }
 
     if (_gen == "pwpb") {
-      _gen_deps = []
-      if (defined(invoker.deps)) {
-        _gen_deps = process_file_template(invoker.deps, "{{source}}_${_gen}")
-      }
-
       _pw_pwpb_proto_library(_lang_target) {
         forward_variables_from(invoker, _forwarded_vars)
         protos = invoker.sources