jbd2: fix a kernel-doc markup

jbd2: fix a kernel-doc markup

The kernel-doc markup that documents _fc_replay_callback is
missing an asterisk, causing this warning:

	../include/linux/jbd2.h:1271: warning: Function parameter or member 'j_fc_replay_callback' not described in 'journal_s'

When building the docs.

Fixes: 609f928af48f ("jbd2: fast commit recovery path")
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
Link: https://lore.kernel.org/r/6055927ada2015b55b413cdd2670533bdc9a8da2.1603791716.git.mchehab+huawei@kernel.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>