swscale/x86/rgb2rgb: Make sure COMPILE_TEMPLATE_AVX is defined

Found-by: iive
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libswscale/x86/rgb2rgb.c

@@ -127,6 +127,7 @@ DECLARE_ASM_CONST(8, uint64_t, mul16_mid)    = 0x2080208020802080ULL;
 #undef COMPILE_TEMPLATE_AMD3DNOW
 #define COMPILE_TEMPLATE_MMXEXT 0
 #define COMPILE_TEMPLATE_SSE2 0
+#define COMPILE_TEMPLATE_AVX 0
 #define COMPILE_TEMPLATE_AMD3DNOW 1
 #define RENAME(a) a ## _3dnow
 #include "rgb2rgb_template.c"