afs: Fix missing wire-up of afs_retry_request()

afs_retry_request() is supposed to be pointed to by the afs_req_ops netfs
operations table, but the pointer got lost somewhere.  The function is used
during writeback to rotate through the authentication keys that were in
force when the file was modified locally.

Fix this by adding the pointer to the function.

Fixes: 1ecb146f ("netfs, afs: Use writeback retry to deal with alternate keys")
Reported-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/1690847.1726346402@warthog.procyon.org.uk


cc: Marc Dionne <marc.dionne@auristor.com>
cc: Jeff Layton <jlayton@kernel.org>
cc: linux-afs@lists.infradead.org
cc: netfs@lists.linux.dev
cc: linux-fsdevel@vger.kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>