If you try to compile this driver on a 64-bit platform then you
will get warnings because it mixes size_t with unsigned int which
only works on 32-bit.

This patch fixes all of the warnings.
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>
Acked-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Tested-by: Corentin Labbe <clabbe.montjoie@gmail.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>