Add comment explaining memset in ArithmeticFPInputs

Change-Id: I1541e3f4629a117eee3f244c0209e442b705b67b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/268844
Auto-Submit: Brian Osman <brianosman@google.com>
Reviewed-by: Brian Osman <brianosman@google.com>
Commit-Queue: Brian Osman <brianosman@google.com>
1 file changed