xfs: update the pag for the last AG at recovery time

Currently log recovery never updates the in-core perag values for the
last allocation group when they were grown by growfs.  This leads to
btree record validation failures for the alloc, ialloc or finotbt
trees if a transaction references this new space.

Found by Brian's new growfs recovery stress test.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Signed-off-by: Carlos Maiolino <cem@kernel.org>