Fix GSVector4i::compare64 function by adjusting the number of iterations
needed to cover the comparison of all the elements of the input arrays,
where the number of bytes to compare is indicated in the size parameter
of the function.
The function is used only in GSdx-TC to compare CLUT arrays.
On one hand this fix closes the recent #2706 and possibly the color
regressions indicated in #2702 (which were both introduced with the new
PaletteMap mechanism, which partially replaced the GSVector4i::update
logic with the bugged GSVector4i::compare64).
On the other hand this might impact long standing wrong texture cache
lookup when palette was involved with 8-bit palette disabled (to be
verified which ones).
Close#2713Fixes#2706Fixes#2715