nfsd: nfsd_file_lease_notifier_call gets a file_lease as an argument

"data" actually refers to a file_lease and not a file_lock. Both structs
have their file_lock_core as the first field though, so this bug should
be harmless without struct randomization in play.

Reported-by: Florian Evers <florian-evers@gmx.de>
Closes: https://bugzilla.kernel.org/show_bug.cgi?id=219008
Fixes: 05580bbf

 ("nfsd: adapt to breakup of struct file_lock")
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Tested-by: Florian Evers <florian-evers@gmx.de>
Signed-off-by: Chuck Lever <chuck.lever@oracle.com>