Fix gRPC buck util not to pickup random .proto files

- should address issue reported in
  https://gerrit.onosproject.org/15958

Change-Id: Id02b950e3a732c89b1c9f71499a6a23b18ad7123
diff --git a/bucklets/grpc.bucklet b/bucklets/grpc.bucklet
index a9e8926..34b31f2 100644
--- a/bucklets/grpc.bucklet
+++ b/bucklets/grpc.bucklet
@@ -90,7 +90,7 @@
     proto_paths = [],
     srcs = [],
     src_string = '', # Useful to build proto files external to the ONOS sources, using BUCK's environment variables.
-    proto_match_patterns = [ "**/proto/**/*.proto" ],
+    proto_match_patterns = [ "src/main/proto/**/*.proto" ],
     protoc_version = DEFAULT_PROTOC_VERSION,
     plugin_version = DEFAULT_GRPC_PLUGIN_VERSION,
     include_std_lib = False,