[S390] cio: channel path memory leak

Move dev_set_name to when we know that the device will actually be
registered in order to avoid a memory leak if the allocated memory
for the channel path has to be freed.

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