ext4: fix comment for s_hash_unsigned

Fix the comment for s_hash_unsigned to not be the opposite of what it
actually is.

Signed-off-by: Eric Biggers <ebiggers@google.com>
Link: https://lore.kernel.org/r/20210527235557.2377525-1-ebiggers@kernel.org


Signed-off-by: Theodore Ts'o <tytso@mit.edu>