cleanup: Fix assembly go vet issues

[Yawning]

# github.com/oasisprotocol/curve25519-voi/curve
curve/edwards_vector_amd64.s:195:1: [amd64] vecConditionalSelect_AVX2: wrong argument size 32; expected $...-28
curve/edwards_vector_amd64.s:201:1: [amd64] vecConditionalSelect_AVX2: invalid VPBROADCASTD of mask+24(FP); uint32 is 4-byte value
curve/window_amd64.s:9:1: [amd64] lookupAffineNiels: wrong argument size 24; expected $...-17
curve/window_amd64.s:135:1: [amd64] lookupCached: wrong argument size 24; expected $...-17

As far as I can tell:

• Argument sizes are an avo issue since it's autogenerating that from the function signature.
• The VPBROADCASTD issue is a go vet bug, because it assumes opcodes use the messed up Go dialect suffixes where D means 8-bytes.

While all of these are annoying, I think it's ok to ignore for now, especially considering that the VPBROADCASTD issue is just a false positive, and I'd rather not edit avo output, so resolving this is blocked on other people fixing their stuff.

[Yawning]

Sigh, my idea of "Ok, I'll just VMOVD the mask first" doesn't make asmdecl shut up either, because of the same issue.

./edwards_vector_amd64.s:201:1: [amd64] vecConditionalSelect_AVX2: invalid VMOVD of mask+24(FP); uint32 is 4-byte value