smb: remove redundant check

->setlease() is never called on non-regular files now. So remove the
check from cifs_setlease().

Link: https://lore.kernel.org/r/170716318935.13976.13465352731929804157@noble.neil.brown.name


Signed-off-by: NeilBrown <neilb@suse.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>