convolve.c: make functions static
convolve.c: make functions static

Change-Id: I764a0e7f4a3b86d3a4c4a2b464e759f2b49bcbed

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