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

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

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