gfs2: Clean up SDF_JOURNAL_LIVE flag handling

gfs2: Clean up SDF_JOURNAL_LIVE flag handling

Change do_withdraw() to clear the SDF_JOURNAL_LIVE flag under the log
flush lock.  In addition, change __gfs2_trans_begin() to check if the
filesystem is already known to be withdrawn using gfs2_withdrawn().
Then, once we are holding the log flush lock, check if the
SDF_JOURNAL_LIVE flag is still set.  This second check ensures that the
filesystem will remain live until the transaction is submitted.

With these changes, it is no longer useful to clear SDF_JOURNAL_LIVE in
gfs2_end_log_write() after calling gfs2_withdraw().

Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>