avdevice/decklink_dec: mark get_frame_timecode and get_bmd_timecode static
The function is not used anywhere else and is causing mingw-w64 clang
builds to fail with
ffmpeg-git/libavdevice/decklink_dec.cpp:792:5: error: no previous prototype for function 'get_bmd_timecode' [-Werror,-Wmissing-prototypes]
int get_bmd_timecode(AVFormatContext *avctx, AVTimecode *tc, AVRational frame_rate, BMDTimecodeFormat tc_format, IDeckLinkVideoInputFrame *videoFrame)
Signed-off-by: Christopher Degawa <ccom@randomderp.com> Signed-off-by: Marton Balint <cus@passwd.hu>