rapidio: fix new kernel-doc warnings

Fix new rapidio kernel-doc warnings:

  Warning(drivers/rapidio/rio-scan.c:953): No description found for parameter 'prev'
  Warning(drivers/rapidio/rio-scan.c:953): No description found for parameter 'prev_port'

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Cc: Alexandre Bounine <alexandre.bounine@idt.com>
Cc: Matt Porter <mporter@kernel.crashing.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>