GFS2: Fix allocation error bug with recursive rgrp glocking

Before this patch function gfs2_write_begin, upon discovering an
error, called gfs2_trim_blocks while the rgrp glock was still held.
That's because gfs2_inplace_release is not called until later.
This patch reorganizes the logic a bit so gfs2_inplace_release
is called to release the lock prior to the call to gfs2_trim_blocks,
thus preventing the glock recursion.

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