Update members of cloud-provider-gcp-maintainers

remove sdmodi who left the GKE team.
add mmamczur, member of the team that owns service controller part of cloupd-provider-gcp

Author: mmamczur

config/kubernetes/org.yaml

@@ -1352,7 +1352,7 @@ teams:
     - jpbetz
     - jprzychodzen
     - mskrocki
-    - sdmodi
+    - mmamczur
     privacy: closed
     repos:
       cloud-provider-gcp: write