Fix WelsHadamardQuant2x2*_AArch64_neon

In WelsHadamardQuant2x2SkipKernel_AArch64_neon, write the output
of cmhi into v0 - this is the register that is assumed to hold
the output.

In WelsHadamardQuant2x2_AArch64_neon, subtract the count of zero
elements from 4, not from 16.

This makes the encoding unit tests pass again.

Review at https://rbcommons.com/s/OpenH264/r/624/.