lavfi: rename vf_split.c -> f_split.c

The file now contains both an audio and a video split filter.

libavfilter/Makefile

@@ -50,7 +50,7 @@ OBJS-$(CONFIG_AMERGE_FILTER)                 += af_amerge.o
 OBJS-$(CONFIG_ANULL_FILTER)                  += af_anull.o
 OBJS-$(CONFIG_ARESAMPLE_FILTER)              += af_aresample.o
 OBJS-$(CONFIG_ASHOWINFO_FILTER)              += af_ashowinfo.o
-OBJS-$(CONFIG_ASPLIT_FILTER)                 += vf_split.o
+OBJS-$(CONFIG_ASPLIT_FILTER)                 += f_split.o
 OBJS-$(CONFIG_ASTREAMSYNC_FILTER)            += af_astreamsync.o
 OBJS-$(CONFIG_ASYNCTS_FILTER)                += af_asyncts.o
 OBJS-$(CONFIG_EARWAX_FILTER)                 += af_earwax.o
@@ -108,7 +108,7 @@ OBJS-$(CONFIG_SETSAR_FILTER)                 += vf_aspect.o
 OBJS-$(CONFIG_SETTB_FILTER)                  += vf_settb.o
 OBJS-$(CONFIG_SHOWINFO_FILTER)               += vf_showinfo.o
 OBJS-$(CONFIG_SLICIFY_FILTER)                += vf_slicify.o
-OBJS-$(CONFIG_SPLIT_FILTER)                  += vf_split.o
+OBJS-$(CONFIG_SPLIT_FILTER)                  += f_split.o
 OBJS-$(CONFIG_SUPER2XSAI_FILTER)             += vf_super2xsai.o
 OBJS-$(CONFIG_SWAPUV_FILTER)                 += vf_swapuv.o
 OBJS-$(CONFIG_THUMBNAIL_FILTER)              += vf_thumbnail.o

libavfilter/f_split.c

@@ -20,7 +20,7 @@
 
 /**
  * @file
- * Video splitter
+ * audio and video splitter
  */
 
 #include "avfilter.h"