mesa/main: Fix overflow in validation of DispatchComputeGroupSizeARB

mesa/main: Fix overflow in validation of DispatchComputeGroupSizeARB

An uint64_t can store the result of multiplying two GLuint (uint32_t),
so use that property to check for overflow when calculating the total.

Change the error message so we don't need to care about the actual
total -- which means we don't need a larger than 64-bit value to hold
it.

Fixes: 45ab63c0cb2 ("mesa/main: add support for ARB_compute_variable_groups_size")
Reviewed-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Tested-by: Marge Bot <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4240>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/4240>