gfs2: Get rid of duplicate log head lookup

Currently at mount time, the recovery code looks up the current log head
and, if necessary, replays the log and writes a recovery header to
indicate that the log is clean.  It does that for each log that may need
recovery.  We also know that our own log will always be checked as part
of that process.  Then, the mount code looks up the log head of our own
log again.

The double log head lookup can be costly, but more importantly, it is
unnecessary because we can trivially compute the position of the log
head after recovery; all we need to do for that is bump the position and
lh_sequence by one when writing a recovery header.

With that in mind, move the call to gfs2_log_pointers_init() into
gfs2_recover_func() and get rid of the double lookup in
gfs2_make_fs_rw().

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