If an error occurs on opcontrol start, the event and per cpu buffers
are released.  If later opcontrol shutdown is called then the free
function will be called again to free buffers that no longer
exist.  This results in a kernel oops.  The following changes
prevent the call to delete buffers that don't exist.
Signed-off-by: NCarl Love <carll@us.ibm.com>
Signed-off-by: NArnd Bergmann <arnd@arndb.de>
Acked-by: NRobert Richter <robert.richter@amd.com>
Signed-off-by: NPaul Mackerras <paulus@samba.org>