GFS2: Fix gfs2_replay_incr_blk for multiple journal sizes

Before this patch, if you used gfs2_jadd to add new journals of a
size smaller than the existing journals, replaying those new journals
would withdraw. That's because function gfs2_replay_incr_blk was
using the number of journal blocks (jd_block) from the superblock's
journal pointer. In other words, "My journal's max size" rather than
"the journal we're replaying's size." This patch changes the function
to use the size of the pertinent journal rather than always using the
journal we happen to be using.

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