s390/tape: fix MTIOCGET ioctl to report blocksize

Remove tape_state from status register and report the drive's current
setting for block size instead as known from other tapes.
Density is not supported so nothing to report here.

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