utils/gcm-ref (present_gf_pmull): Round width up to a multiple of 64 bits.

utils/gcm-ref (present_gf_pmull): Round width up to a multiple of 64 bits.

Otherwise the later loop, which pulls off 64-bit chunks, gets badly
confused.

Now `gcm-ref' can actually calculate all of the things properly.

	for p in pclmul vmullp64 pmull; do
	  while read u v; do utils/gcm-ref $p $u $v || break 2; done <<EOF
	cde4bef260d7bcda 163547d348b75511
	cde4bef260d7bcda163547d3 48b7551195e77022907dd1df
	cde4bef260d7bcda163547d348b75511 95e77022907dd1dff7dac5c9941d26d0
	cde4bef260d7bcda163547d348b7551195e77022907dd1df f7dac5c9941d26d0c6eb14ad568f86edd1dc9268eeee5332
	cde4bef260d7bcda163547d348b7551195e77022907dd1dff7dac5c9941d26d0 c6eb14ad568f86edd1dc9268eeee533285a6ed810c9b689daaa9060d2d4b6003
	EOF
	done

I wonder what this means about the changes coming up...