[S390] dasd: fix message flood for unsolicited interrupts

In the unsolicited interupt handler fake IRBs from CIO have to be
ignored because there is nothing to do.
The function dump_sense should not be called if there is no sense
data available.

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