rapidio: fix kerneldoc warnings after DMA support was added

Signed-off-by: Alexandre Bounine <alexandre.bounine@idt.com>
Reported-by: Robert P. J. Day <rpjday@crashcourse.ca>
Cc: Robert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>