[PATCH] s390: use normal switch statement for ioctls in dasd_ioctlc

Handle ioctls implemented in dasd_ioctl through the normal switch statement
that most drivers use instead of the awkward dasd_ioctl_no_register routine.
This avoids searching a linear list on every call to dasd_ioctl(), and allows
to give the various ioctl implementation functions sane prototypes, aswell as
moving the check for bdev->bd_disk->private_data from the individual functions
to dasd_ioctl.  (I think it can't actually every be NULL, but let's keep that
for later)

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>