Fix Makefile build

Makefile

@@ -5,7 +5,7 @@ CHART_DIR = $(SELF_DIR)charts/nginx-gateway-fabric
 NGINX_CONF_DIR = internal/mode/static/nginx/conf
 NJS_DIR = internal/mode/static/nginx/modules/src
 KIND_CONFIG_FILE = $(SELF_DIR)config/cluster/kind-cluster.yaml
-NGINX_DOCKER_BUILD_PLUS_ARGS = --secret id=nginx-repo.crt,src=nginx-repo.crt --secret id=nginx-repo.key,src=nginx-repo.key
+NGINX_DOCKER_BUILD_PLUS_ARGS = --secret id=nginx-repo.crt,src=$(SELF_DIR)nginx-repo.crt --secret id=nginx-repo.key,src=$(SELF_DIR)nginx-repo.key
 BUILD_AGENT = local
 
 PROD_TELEMETRY_ENDPOINT = oss.edge.df.f5.com:443