gfs2: leaf_dealloc needs to allocate one more revoke

Function leaf_dealloc was not allocating enough journal space for
revokes. Before, it allocated 'l_blocks' revokes, but it needs one
more for the revoke of the dinode that is modified. This patch adds
the needed revoke entry to function leaf_dealloc.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>