mmc: au1xmmc.c: use resource_size()

[cjb: rebased patch against Linus]
Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Cc: <linux-mmc@vger.kernel.org>
Acked-by: Manuel Lauss <manuel.lauss@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Chris Ball <cjb@laptop.org>