build: fix centos 8 steam build install-dep

make install-dep sometimes failed at
downloading metadata for repository 'powertools-source':
disable unnecessary powertools-source repo.

Type: fix
Fixes: 1affb31ef528 ("build: fix centos-8 'make install-deps'")
Signed-off-by: Tianyu Li <tianyu.li@arm.com>
Change-Id: I481d6106eea38190b3ddd79e8614b2ead7130807
diff --git a/Makefile b/Makefile
index def06a3..6583a29 100644
--- a/Makefile
+++ b/Makefile
@@ -324,7 +324,7 @@
 else ifeq ($(OS_ID)-$(OS_VERSION_ID),centos-8)
 	@sudo -E dnf install $(CONFIRM) dnf-plugins-core epel-release
 	@sudo -E dnf config-manager --set-enabled \
-          $(shell dnf repolist all 2>/dev/null|grep -i powertools|cut -d' ' -f1)
+          $(shell dnf repolist all 2>/dev/null|grep -i powertools|cut -d' ' -f1|grep -v source)
 	@sudo -E dnf groupinstall $(CONFIRM) $(RPM_DEPENDS_GROUPS)
 	@sudo -E dnf install --skip-broken $(CONFIRM) $(RPM_DEPENDS)
 else ifeq ($(OS_ID),centos)