x86/hevc_idct: add a colon to labels

This fixes a warning spam when using NASM
Signed-off-by: James Almer <jamrial@gmail.com>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavcodec/x86/hevc_idct.asm

@@ -36,7 +36,7 @@ cglobal hevc_idct%1x%1_dc_%3, 1, 2, 1, coeff, tmp
     SPLATW              m0, xm0
     DEFINE_ARGS coeff, cnt
     mov               cntd, %2
-.loop
+.loop:
     mova [coeffq+mmsize*0], m0
     mova [coeffq+mmsize*1], m0
     mova [coeffq+mmsize*2], m0