dsp.h: bump msvc arm64 version requirement to 16.6

there was a bug in 16.4 causing compile failures with vtbl4_u8():

src\dsp\lossless_neon.c(105): error C2143: syntax error: missing ')'
before '{'
src\dsp\lossless_neon.c(105): error C2168: 'neon_tbl2_q8': too few
actual parameters for intrinsic function

https://developercommunity.visualstudio.com/t/cannot-compile-arm64-neon-vtbl4-u8-function-in-c-f/859331

Change-Id: I87c21850b3c597aa5cb41a8105b81e2135a9f890
1 file changed