afs: Fix leak of ungot volume

afs: Fix leak of ungot volume

Fix afs_lookup_volume_rcu() so that it doesn't leak a dying volume if
afs_try_get_volume() fails.

Fixes: 32222f09782f ("afs: Apply server breaks to mmap'd files in the call processor")
Closes: https://sashiko.dev/#/patchset/20260609081738.770127-1-dhowells%40redhat.com
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://patch.msgid.link/20260622090856.2746629-17-dhowells@redhat.com
cc: Marc Dionne <marc.dionne@auristor.com>
cc: Deepakkumar Karn <dkarn@redhat.com>
cc: linux-afs@lists.infradead.org
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>