cas: validate shared buffer size before using

bug: 67962232

test:
cts MediaCasTest
vts VtsHalCasV1_0Target

Change-Id: I20b89d5971db4c89704245bb00c281af8c943697
(cherry picked from commit 16a3cd0b0729bd53265897cf8c790013156e92ce)
1 file changed