Speed up data-transfer between Host and Device

Try moving you `clEnqueueUnmapMemObject` call before launching your kernel. From the opencl documentation (https://www.khronos.org/registry/opencl/sdk/1.0/docs/man/xhtml/clenqueuemapbuffer.html):

"The contents of the regions of a memory object mapped for writing (i.e. CL_MAP_WRITE is set in map_flags argument to clEnqueueMapBuffer or clEnqueueMapImage) are considered to be undefined until this region is unmapped. Reads and writes by a kernel executing on a device to a memory region(s) mapped for writing are undefined."