[S390] user space fault: report fault before calling do_exit

Report user space faults before calling do_exit, since do_exit does
not return and therefore we will never see the fault message on the
console.

Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>