[S390] vmlogrdr function annotation.

Use __init and __exit for vmlogrdr. Both functions are only referenced
by the module_init exit macros, so this change should be fine.

Acked-by: Stefan Weinhuber <wein@de.ibm.com>
Signed-off-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>