[SCSI] sg: remove while (1) non-loop

The while (1) construct isn't actually a loop at all.  So let's not
pretent and obfuscate the code.

Signed-off-by: Joern Engel <joern@logfs.org>
Acked-by: Douglas Gilbert <dgilbert@interlog.com>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>