[S390] drivers/s390/block/dasd_eckd.c: add missing dasd_sfree_request

Extend some error paths to call dasd_sfree_request as done earlier in the
function.  The error-handling code is also moved to the end of the function.

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>