CIP: Bump version suffix to -cip28 after Renesas patches

Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
diff --git a/localversion-cip b/localversion-cip
index d5ae26e..72a88e3 100644
--- a/localversion-cip
+++ b/localversion-cip
@@ -1 +1 @@
--cip27
+-cip28