Bump MODULE_VERSION to 5.2.1

Change-Id: I73b42c27dfb256818f650d090586fe8bc7db6a2c
Reviewed-by: Matti Paaso <matti.paaso@digia.com>
Reviewed-by: Oswald Buddenhagen <oswald.buddenhagen@digia.com>
Reviewed-by: Alex Blasche <alexander.blasche@digia.com>