avcodec/Makefile: Unconditionally skip vulkan_video_codec_av1std.h

libavcodec/vulkan_video_codec_av1std.h currently does not pass
checkheaders: It is missing stdint.h and vulkan/vulkan_core.h.
The comment "This header is NOT YET generated from the Khronos Vulkan
XML API Registry." as well as the fact that it does not use our standard
inclusion guards makes the file appear as if it is to be treated
like a third-party header and not one of our own. This commit
therefore "fixes" the issue by unconditionally skipping said header.

Reviewed-by: Lynne <dev@lynne.ee>
Signed-off-by: Andreas Rheinhardt <andreas.rheinhardt@outlook.com>

libavcodec/Makefile

@@ -1283,6 +1283,7 @@ SKIPHEADERS                            += %_tablegen.h                  \
                                           aacenc_quantization.h         \
                                           aacenc_quantization_misc.h    \
                                           bitstream_template.h          \
+                                          vulkan_video_codec_av1std.h   \
                                           $(ARCH)/vpx_arith.h          \
 
 SKIPHEADERS-$(CONFIG_AMF)              += amfenc.h
@@ -1304,7 +1305,7 @@ SKIPHEADERS-$(CONFIG_XVMC)             += xvmc.h
 SKIPHEADERS-$(CONFIG_VAAPI)            += vaapi_decode.h vaapi_hevc.h vaapi_encode.h
 SKIPHEADERS-$(CONFIG_VDPAU)            += vdpau.h vdpau_internal.h
 SKIPHEADERS-$(CONFIG_VIDEOTOOLBOX)     += videotoolbox.h vt_internal.h
-SKIPHEADERS-$(CONFIG_VULKAN)           += vulkan.h vulkan_video.h vulkan_decode.h vulkan_video_codec_av1std.h vulkan_video_codec_av1std_decode.h
+SKIPHEADERS-$(CONFIG_VULKAN)           += vulkan.h vulkan_video.h vulkan_decode.h vulkan_video_codec_av1std_decode.h
 SKIPHEADERS-$(CONFIG_V4L2_M2M)         += v4l2_buffers.h v4l2_context.h v4l2_m2m.h
 SKIPHEADERS-$(CONFIG_ZLIB)             += zlib_wrapper.h