xfs: fix the zoned RT growfs check for zone alignment

xfs: fix the zoned RT growfs check for zone alignment

The grofs code for zoned RT subvolums already tries to check for zone
alignment, but gets it wrong by using the old instead of the new mount
structure.

Fixes: 01b71e64bb87 ("xfs: support growfs on zoned file systems")
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Cc: stable@vger.kernel.org # v6.15
Signed-off-by: Carlos Maiolino <cem@kernel.org>