cogl-bitmap: Remove const from premult_alpha_last_four_pixels_sse2
cogl-bitmap: Remove const from premult_alpha_last_four_pixels_sse2

The function modifies the pixels pointed by p in-place so the pointer
can not be constant. The compiler was accepting this because the
modification is done from inline assembler.

djdeath/cogl-android,spatulasnout/cogl,djdeath/cogl-android,djdeath/cogl-android,gcampax/cogl,djdeath/cogl,Distrotech/cogl,gcampax/cogl,djdeath/cogl,collects/cogl,Distrotech/cogl,djdeath/cogl,collects/cogl,gcampax/cogl,Distrotech/cogl,Distrotech/cogl,spatulasnout/cogl,gcampax/cogl