adding PLUGIN_DIR

Signed-off-by: Youssef Kandil <youssefkandil@aucegypt.edu>

clockgating-plugin/Makefile

diff --git a/clockgating-plugin/Makefile b/clockgating-plugin/Makefile
index 16937fa..5b4219e 100644
--- a/clockgating-plugin/Makefile
+++ b/clockgating-plugin/Makefile
@@ -14,6 +14,8 @@
 #
 # SPDX-License-Identifier: Apache-2.0
 
+PLUGIN_DIR := $(abspath $(dir $(lastword $(MAKEFILE_LIST))))
+
 NAME = reg_clock_gating
 SOURCES = reg_clock_gating.cc
 include ../Makefile_plugin.common