mp3dec: Disable integer overflow errors in dct_6 and mdct_6

Integer overflow sanitizer errors are now disabled in
pvmp3_dct_6 and pvmp3_mdct_6 like other variants

Bug: 136053885
Test: poc in bug
Test: atest Mp3DecoderTest -- --enable-module-dynamic-download=true

Change-Id: I5afca806e2b7090333c88f07fd15e1ee99885b0b