Use major version for rocky in cinc-installer.sh

This commit fixes a bug from aws#2992
This commit makes the code behave similar between rocky and el(redhat)

Signed-off-by: Hanwen <[email protected]>

Author: hanwen-cluster

util/cinc-install.sh

@@ -579,6 +579,9 @@ case $platform in
     # FIXME:  "el" is deprecated, should use "redhat"
     platform_version=$major_version
     ;;
+  "rocky")
+    platform_version=$major_version
+    ;;
   "debian")
     if test "x$major_version" = "x5"; then
       # This is here for potential back-compat.