gfs2: gfs2_stuffed_write_end cleanup

First, change the sanity check in gfs2_stuffed_write_end to check for
the actual write size instead of the requested write size.

Second, use the existing teardown code in gfs2_write_end instead of
duplicating it in gfs2_stuffed_write_end.

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