rapidio: adjust 12 checks for null pointers

rapidio: adjust 12 checks for null pointers

checkpatch pointed information out like the following.

  Comparison to NULL could be written ...

Thus fix the affected source code places.

Link: http://lkml.kernel.org/r/739f9f1c-3ebe-c21b-c5e2-31976cfbc0ee@users.sourceforge.net
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Acked-by: Alexandre Bounine <alexandre.bounine@idt.com>
Cc: Matt Porter <mporter@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>