[S390] return 'count' for successful execution of dasd_eer_enable.

Currently the return value of 'dasd_eer_enable' is returned - even if the
function returned '0'. Now return 'count' for successful execution.

Signed-off-by: Horst Hummel <horst.hummel@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>