x86: Fix an alignment issue in 8-bit AVX-512 loop restoration

We don't have a separate 8-bit AVX-512 5-tap Wiener filter so the 7-tap
function is used for chroma as well, and in some esoteric edge cases
chroma dst pointers may only have a 32-byte alignment despite having
a width larger than 32, so use an unaligned store as a workaround.