scsi: libosd: Remove VLA usage

scsi: libosd: Remove VLA usage

On the quest to remove all VLAs from the kernel[1] this rearranges the
code to avoid a VLA warning under -Wvla (gcc doesn't recognize "const"
variables as not triggering VLA creation). Additionally cleans up
variable naming to avoid 80 character column limit.

[1] https://lkml.kernel.org/r/CA+55aFzCG-zNmZwX4A2FQpadafLfEzK6CC=qPXydAacU1RqZWA@mail.gmail.com

Signed-off-by: Kees Cook <keescook@chromium.org>
Acked-by: Boaz Harrosh <ooo@electrozaur.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>