avdevice/decklink_dec: remove extra bracket

Fixes compilation broken in 2245476e

Fixes ticket #6791
Signed-off-by: James Almer <jamrial@gmail.com>

libavdevice/decklink_dec.cpp

@@ -959,7 +959,7 @@ av_cold int ff_decklink_read_header(AVFormatContext *avctx)
 
     st->time_base.den      = ctx->bmd_tb_den;
     st->time_base.num      = ctx->bmd_tb_num;
-    st->r_frame_rate       = av_make_q(st->time_base.den, st->time_base.num));
+    st->r_frame_rate       = av_make_q(st->time_base.den, st->time_base.num);
 
     switch((BMDPixelFormat)cctx->raw_format) {
     case bmdFormat8BitYUV: