[S390] dasd: prevent panic with unresumed devices

If a device is not resumed correctly the system crashes when this
device is set offline. This may happen if it gets disconnected
during suspend.
Check if the device is already removed from alias handling and skip
these steps to prevent the kernel panic.

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