qseecom: check error return value of ion_map_kernel

ion_map_kernel() is called without checking for or acting upon the
possible error conditions this function may return, make change to
check its error return value.

CRs-fixed: 1081637
Change-Id: I0a34f0bbc9f2049b826777a31e14d2cf62cdc211
Signed-off-by: Zhen Kong <zkong@codeaurora.org>