lavc/Makefile: build vulkan decode code if vulkan_av1 has been enabled

Forgotten.

Reviewed-by: Neal Gompa <ngompa13@gmail.com>
Tested-by: Neal Gompa <ngompa13@gmail.com>
(cherry picked from commit 8c117b75af)

libavcodec/Makefile

@@ -993,7 +993,7 @@ OBJS-$(CONFIG_AV1_DXVA2_HWACCEL)          += dxva2_av1.o
 OBJS-$(CONFIG_AV1_NVDEC_HWACCEL)          += nvdec_av1.o
 OBJS-$(CONFIG_AV1_VAAPI_HWACCEL)          += vaapi_av1.o
 OBJS-$(CONFIG_AV1_VDPAU_HWACCEL)          += vdpau_av1.o
-OBJS-$(CONFIG_AV1_VULKAN_HWACCEL)         += vulkan_av1.o
+OBJS-$(CONFIG_AV1_VULKAN_HWACCEL)         += vulkan_decode.o vulkan_av1.o
 OBJS-$(CONFIG_H263_VAAPI_HWACCEL)         += vaapi_mpeg4.o
 OBJS-$(CONFIG_H263_VIDEOTOOLBOX_HWACCEL)  += videotoolbox.o
 OBJS-$(CONFIG_H264_D3D11VA_HWACCEL)       += dxva2_h264.o