arm: dma-mapping: fix data types to hold size_t

size_t type data should not be held under int, this can
truncate large values especially on a 64bit system,
fix it.

Change-Id: I5ad1ab321738772a99920e3fa287bda266cb05ed
Signed-off-by: Shiraz Hashim <shashim@codeaurora.org>