jbd2: make jbd2_journal_get_max_txn_bufs() internal

jbd2: make jbd2_journal_get_max_txn_bufs() internal

There's no reason to have jbd2_journal_get_max_txn_bufs() public
function. Currently all users are internal and can use
journal->j_max_transaction_buffers instead. This saves some unnecessary
recomputations of the limit as a bonus which becomes important as this
function gets more complex in the following patch.

CC: stable@vger.kernel.org
Signed-off-by: Jan Kara <jack@suse.cz>
Reviewed-by: Zhang Yi <yi.zhang@huawei.com>
Link: https://patch.msgid.link/20240624170127.3253-1-jack@suse.cz
Signed-off-by: Theodore Ts'o <tytso@mit.edu>