devices can be opened multiple times simultaneously but we're
expected to be able to do so by the rest of the loader.
This fixes booting from disks attached to the on-board SCSI
controller of Sun Ultra 1 (previously this triggered a trap)
and probably also of AX1115 boards.
- While here, remove unused variables and add empty lines where
style(9) requires such.
Tested on: powerpc (grehan), sparc64
MFC after: 1 month
3727af6a8b