afs: Fix file locking

Fix AFS file locking to use the correct vnode pointer and remove a member
of the afs_operation struct that is never set, but it is read and followed,
causing an oops.

This can be triggered by:

	flock -s /afs/example.com/foo sleep 1

when it calls the kernel to get a file lock.

Fixes: e49c7b2f ("afs: Build an abstraction around an "operation" concept")
Reported-by: Dave Botsch <botsch@cnf.cornell.edu>
Signed-off-by: David Howells <dhowells@redhat.com>
Tested-by: Dave Botsch <botsch@cnf.cornell.edu>

fs/afs/flock.c

@@ -71,7 +71,7 @@ static void afs_schedule_lock_extension(struct afs_vnode *vnode)
 void afs_lock_op_done(struct afs_call *call)
 {
 	struct afs_operation *op = call->op;
-	struct afs_vnode *vnode = op->lock.lvnode;
+	struct afs_vnode *vnode = op->file[0].vnode;
 
 	if (call->error == 0) {
 		spin_lock(&vnode->lock);

fs/afs/internal.h

@@ -795,7 +795,6 @@ struct afs_operation {
 			struct afs_read *req;
 		} fetch;
 		struct {
-			struct afs_vnode *lvnode;	/* vnode being locked */
 			afs_lock_type_t type;
 		} lock;
 		struct {