mkfs: fix copy-paste error in calculate_rtgroup_geometry

mkfs: fix copy-paste error in calculate_rtgroup_geometry

Fix this copy-paste error -- we should calculate the rt volume
concurrency either if the user gave us an explicit option, or if they
didn't but the rt volume is an SSD.

Cc: linux-xfs@vger.kernel.org # v6.13.0
Fixes: 34738ff0ee80de ("mkfs: allow sizing realtime allocation groups for concurrency")
Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>