afs: Fix server->active leak in afs_put_server

afs: Fix server->active leak in afs_put_server

The atomic_read was accidentally replaced with atomic_inc_return,
which prevents the server from getting cleaned up and causes rmmod
to hang with a warning:

    Can't purge s=00000001

Fixes: 2757a4dc1849 ("afs: Fix access after dec in put functions")
Signed-off-by: Marc Dionne <marc.dionne@auristor.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20221130174053.2665818-1-marc.dionne@auristor.com/
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>