[S390] tape: Fix medium state handling

Currently there are situations, where the tape medium state (loaded, unloaded,
unknown) is not set correctly. The reason is that the medium association
field is used to determine the medium state. This not always leads to
correct results. To fix that we use another field of the medium sense
data instead.

Signed-off-by: Michael Holzheu <holzheu@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>