[S390] dasd: Correct retry counter for terminated I/O.

In case the DASD driver needs to term a running I/O the retry counter
is decreased twice.
Remove the unnecessary retry counter decrease in das_term_IO.

Signed-off-by: Stefan Haberland <stefan.haberland@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>