s390/eadm: change timeout value

Tests have shown that 5 seconds is sometimes not enough for an IRQ
to arrive (especially when the device is doing garbage collection).
Let's wait a little longer.

Signed-off-by: Sebastian Ott <sebott@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>