avformat/mp3dec: replace SAME_HEADER_MASK with MP3_MASK

avformat/mp3dec: replace SAME_HEADER_MASK with MP3_MASK

mp3 header bitstream syntax:
header()
{
    syncword   12bits bslsf
    id         1bit    bslsf
    layer      2bit    bslsf
    protection_bit 1bit bslsf
    bitrate_index 4bits bslsf
    sampling_frequency 2bits bslsf
    padding_bit  1bit bslsf
    private_bit 1bit bslsf
    mode 2bits bslsf
    mode_extension 2bits bslsf
    copyright 1bit bslsf
    original/home 1bit bslsf
    emphasis 2bits bslsf
}

if the header is masking with MP3_MASK(0xFFFE0CCF), below fields will be cleared:
protection_bit, bitrate_index, sampling_freqency, mode

with SAME_HEADER_MASK(0xFFFE0C00), extra below fields will be cleared which didn't make
sense:
mode_extension, copyright, original/home, emphasis

As the MP3_MASK is good for same mp3 header masking and is defined in the
header, so it's preferable to remove SAME_HEADER_MASK to keep the masking same.

Signed-off-by: Limin Wang <lance.lmwang@gmail.com>
Signed-off-by: Michael Niedermayer <michael@niedermayer.cc>