gfs2: freeze should work on read-only mounts

Before this patch, function freeze_go_sync, called when promoting
the freeze glock, was testing for the SDF_JOURNAL_LIVE superblock flag.
That's only set for read-write mounts. Read-only mounts don't use a
journal, so the bit is never set, so the freeze never happened.

This patch removes the check for SDF_JOURNAL_LIVE for freeze requests
but still checks it when deciding whether to flush a journal.

Signed-off-by: Bob Peterson <rpeterso@redhat.com>