shaderInt8Int16-shift: Ensure the shift counts will produce the failure

In 7d03ddcc, the shift counts for int16_t did not have 0x10 set, so the bug would not be reproduced. With this change to the test, I have verified that func.shader.shift.int16_t fails on BDW and ICL. Based on that, I assume it will fail on other platforms as well.

Fixes: 7d03ddcc ("Test shift counts for int8_t and int16_t that are too large w/ explicit masks")