xfs: don't nest icloglock inside ic_callback_lock

It's completely unnecessary because callbacks are added to iclogs
without holding the icloglock, hence no amount of ordering between
the icloglock and ic_callback_lock will order the removal of
callbacks from the iclog.

Signed-off-by: Dave Chinner <dchinner@redhat.com>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Signed-off-by: Darrick J. Wong <djwong@kernel.org>