xfs: use the recalculated transaction reservation in xfs_growfs_rt_bmblock
After going great length to calculate the transaction reservation for
the new geometry, we should also use it to allocate the transaction it
was calculated for.
Fixes: 578bd4ce7100 ("xfs: recompute growfsrtfree transaction reservation while growing rt volume") Signed-off-by: Christoph Hellwig <hch@lst.de> Reviewed-by: Darrick J. Wong <djwong@kernel.org> Signed-off-by: Darrick J. Wong <djwong@kernel.org>