loader: GELI encrypted disk should still use device name disk

geli_probe_and_attach() does pick geli_devsw structure for
encrypted disks, the implementation depends on device
name "disk" when device type is DEVT_DISK, but geli_devsw is
setting name field "gelidisk".

PR: 264282
Submitted by: yamagi@yamagi.org
Reported by: yamagi@yamagi.org
MFC after: 2 weeks