ide-cd: convert cdrom_decode_status() to use switch statements

Based on earlier work by Borislav Petkov.

Convert cdrom_decode_status() to use switch statements in
preparation to unify handling of fs and pc requests.

While at it:
- remove superfluous comments and do minor CodingStyle fixups

There should be no functional changes caused by this patch.

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: Borislav Petkov <petkovbb@gmail.com>
Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>