avfilter: x86: consistent filenames for filter optimizations

libavfilter/x86/Makefile

-OBJS-$(CONFIG_GRADFUN_FILTER)                += x86/gradfun.o
+OBJS-$(CONFIG_GRADFUN_FILTER)                += x86/vf_gradfun.o
 OBJS-$(CONFIG_HQDN3D_FILTER)                 += x86/vf_hqdn3d_init.o
 OBJS-$(CONFIG_VOLUME_FILTER)                 += x86/af_volume_init.o
-OBJS-$(CONFIG_YADIF_FILTER)                  += x86/yadif_init.o
+OBJS-$(CONFIG_YADIF_FILTER)                  += x86/vf_yadif_init.o
 
-YASM-OBJS-$(CONFIG_HQDN3D_FILTER)            += x86/hqdn3d.o
+YASM-OBJS-$(CONFIG_HQDN3D_FILTER)            += x86/vf_hqdn3d.o
 YASM-OBJS-$(CONFIG_VOLUME_FILTER)            += x86/af_volume.o
-YASM-OBJS-$(CONFIG_YADIF_FILTER)             += x86/yadif.o
+YASM-OBJS-$(CONFIG_YADIF_FILTER)             += x86/vf_yadif.o