avfilter/vf_vqe_amf: leave the output colorspace untouched

The shared output path retags every frame from the filter's
color_profile unless that is AMF_VIDEO_CONVERTER_COLOR_PROFILE_UNKNOWN,
which is -1. vqe_amf never set it, so the zero-initialized field read as
AMF_VIDEO_CONVERTER_COLOR_PROFILE_601 and every enhanced frame came out
tagged SMPTE 170M, whatever the input said. The enhancer does no colour
conversion and has no colour option, so set the profile to unknown at
init, as frc_amf already does, and the copied colorspace stays.

Tested on Windows 11, RX 9070 XT, driver 32.0.31041.1004: BT.709 input
through vqe_amf is reported as smpte170m by showinfo before and as bt709
after.

Assisted-by: Claude Fable 5.1
Signed-off-by: Julius Bairaktaris <julius@bairaktaris.de>

libavfilter/vf_vqe_amf.c

@@ -55,6 +55,7 @@ static int amf_vqe_init(AVFilterContext *avctx) {
     AMFVQEFilterContext *ctx = avctx->priv;
 
     ctx->common.format = AV_PIX_FMT_NONE;
+    ctx->common.color_profile = AMF_VIDEO_CONVERTER_COLOR_PROFILE_UNKNOWN;
     ctx->common.shader_input = 1;
 
     return 0;