gfs2: fix freeze error handling

gfs2: fix freeze error handling

After commit b77b4a4815a9 ("gfs2: Rework freeze / thaw logic"),
the freeze error handling is broken because gfs2_do_thaw()
overwrites the 'error' variable, causing incorrect processing
of the original freeze error.

Fix this by calling gfs2_do_thaw() when gfs2_lock_fs_check_clean()
fails but ignoring its return value to preserve the original
freeze error for proper reporting.

Found by Linux Verification Center (linuxtesting.org) with SVACE.

Fixes: b77b4a4815a9 ("gfs2: Rework freeze / thaw logic")
Cc: stable@vger.kernel.org # v6.5+
Signed-off-by: Alexey Velichayshiy <a.velichayshiy@ispras.ru>
Signed-off-by: Andreas Gruenbacher <agruenba@redhat.com>