avcodec/dca: return standard error codes in avpriv_dca_parse_core_frame_header()

This prevents making the DCAParseError enum part of the ABI.

Reviewed-by: Michael Niedermayer <michael@niedermayer.cc>
Reviewed-by: foo86 <foobaz86@gmail.com>
Signed-off-by: James Almer <jamrial@gmail.com>
