[PATCH] s390: dasd reference counting

When using the dasd diag discipline, the base discipline module (eckd or fba)
can be unloaded, even though the dasd driver requires both discipline modules
(base and diag) to work correctly.

Implement reference counting for both base and diag discipline modules in
order to fix this.

Signed-off-by: Peter Oberparleiter <peter.oberparleiter@de.ibm.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>