Use 64-bit math in work group size assertion.

Use 64-bit math in work group size assertion.

If the maximum workgroup size in each dimension is large enough, this
can overflow, causing the comparison to fail.  For example, on Intel
Haswell, we get:

   assert(2048 * 2048 * 2048 > 2048) -> assert(0 > 2048) -> fail

Casting one value to deInt64 causes the multiplications to occur as
64-bit values, so we don't overflow.

Affects:

dEQP-GLES31.functional.debug.negative_coverage.*.compute.invalid_maximum_work_group_sizes

Components: AOSP

Change-Id: Ie03627a378f4fdc46ce241bbdd3693ae829c217d