[S390] qdio: remove the module_get & module_put pair

Increasing the qdio reference count for every used subchannel
is unnecessary since unloading qdio (if build as a module) is
only possible if other modules that use qdio are unloaded.
Unloading modules that use qdio in turn requires that these
modules shut down all qdio subchannels. Therefore the additional
module_get reference is not needed.

Signed-off-by: Jan Glauber <jang@linux.vnet.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>