Update convolve_sse2.c
Update convolve_sse2.c

to process width 4 case separately

Change-Id: I18f5e026927c4d3d705586e9e0f8a6315931951c

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