Declare final_filter_fast_internal as static.
Declare final_filter_fast_internal as static.

final_filter_fast_internal is only used within this file.

Change-Id: Ib95733d8496880fef4004ad5b1f3a29b298710bd

GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom,GrokImageCompression/aom