avcodec/amfenc: Fix inverted loop filter option

The AMF HEVC encoder takes a bool option for whether deblocking filter
should be _disabled_ instead of whether it should _enabled_ like the
AMF H.264 encoder does. The logic was accidentally copied from H.264 to
HEVC without negating the bool value, so the deblocking filter was
actually disabled when AV_CODEC_FLAG_LOOP_FILTER was set.

Before this patch:
------------------
no flags set => deblocking filter on
flags +loop  => deblocking filter off
flags -loop  => deblocking filter on

After this patch:
-----------------
no flags set => deblocking filter on
flags +loop  => deblocking filter on
flags -loop  => deblocking filter off

Signed-off-by: Cameron Gutman <aicommander@gmail.com>

libavcodec/amfenc_hevc.c

@@ -269,7 +269,7 @@ FF_ENABLE_DEPRECATION_WARNINGS
     if (avctx->slices > 1) {
         AMF_ASSIGN_PROPERTY_INT64(res, ctx->encoder, AMF_VIDEO_ENCODER_HEVC_SLICES_PER_FRAME, avctx->slices);
     }
-    AMF_ASSIGN_PROPERTY_BOOL(res, ctx->encoder, AMF_VIDEO_ENCODER_HEVC_DE_BLOCKING_FILTER_DISABLE, deblocking_filter);
+    AMF_ASSIGN_PROPERTY_BOOL(res, ctx->encoder, AMF_VIDEO_ENCODER_HEVC_DE_BLOCKING_FILTER_DISABLE, !deblocking_filter);
 
     if (ctx->header_insertion_mode != -1) {
         AMF_ASSIGN_PROPERTY_INT64(res, ctx->encoder, AMF_VIDEO_ENCODER_HEVC_HEADER_INSERTION_MODE, ctx->header_insertion_mode);
@@ -511,6 +511,7 @@ static const FFCodecDefault defaults[] = {
     { "slices",     "1"   },
     { "qmin",       "-1"  },
     { "qmax",       "-1"  },
+    { "flags",      "+loop"},
     { NULL                },
 };
 static const AVClass hevc_amf_class = {