fs/jbd/revoke.c: replace shift loop by ilog2

journal_init_revoke_table is only called with positive hash_size
(JOURNAL_REVOKE_DEFAULT_HASH) so we can replace loop shift by ilog2

Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Jan Kara <jack@suse.cz>
Cc: Joe Perches <joe@perches.com>
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Jan Kara <jack@suse.cz>