fs-verity: simplify sysctls with register_sysctl()

register_sysctl_paths() is only needed if your child (directories) have
entries but this does not so just use register_sysctl() so to do away
with the path specification.

Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20230302202826.776286-10-mcgrof@kernel.org


Signed-off-by: Eric Biggers <ebiggers@google.com>