common/dpaax: fix physical address conversion

common/dpaax: fix physical address conversion

If some of the VA entries of table are somehow not populated and are
NULL, it can add offset to NULL and return the invalid VA in PA to
VA conversion.

In this patch, adding a check if the VA entry has valid address only
then add offset and return VA.

Fixes: 2f3d633aa593 ("common/dpaax: add library for PA/VA translation table")
Cc: stable@dpdk.org
Signed-off-by: Gagandeep Singh <g.singh@nxp.com>
Signed-off-by: Nipun Gupta <nipun.gupta@nxp.com>
Acked-by: Hemant Agrawal <hemant.agrawal@nxp.com>