When verification of the computed result fails, the test would still
report as "passed". This is because `s_test_fail` is only written to
and never read.
Fix the immediate issue by returning a failure value and incrementing
`gFailCount` if any error was detected. The error handling can be
improved further, but I'm leaving that out of the scope of this fix.
Fixes https://github.com/KhronosGroup/OpenCL-CTS/issues/1445
Signed-off-by: Sven van Haastregt <sven.vanhaastregt@arm.com>