change double to int in coalescing-global to avoid compiler warnings

[rcrovella]

Here:
https://github.com/parallel-forall/code-samples/blob/master/series/cuda-cpp/coalescing-global/coalescing.cu

lines 54 and 70 are passing a double for the second argument:

checkCuda( cudaMemset(d_a, 0.0, n * sizeof(T)) );

This is not really sensible and may trigger compiler warnings like this:

coalescing.cu:70: warning: passing âdoubleâ for argument 2 to âcudaError_t cudaMemset(void*, int, size_t)â

I would recommend changing those 2 instances of 0.0 to just 0