r600g/compute: Fix bug in compute memory pool
r600g/compute: Fix bug in compute memory pool

When adding a new buffer to the beginning of the memory pool, we were
accidentally deleting the buffer that was first in the buffer list.
This was caused by a bug in the memory pool's linked list
implementation.

benaadams/glsl-optimizer,benaadams/glsl-optimizer,jbarczak/glsl-optimizer,wolf96/glsl-optimizer,mcanthony/glsl-optimizer,zz85/glsl-optimizer,metora/MesaGLSLCompiler,djreep81/glsl-optimizer,mapbox/glsl-optimizer,wolf96/glsl-optimizer,djreep81/glsl-optimizer,jbarczak/glsl-optimizer,zeux/glsl-optimizer,zeux/glsl-optimizer,tokyovigilante/glsl-optimizer,wolf96/glsl-optimizer,jbarczak/glsl-optimizer,benaadams/glsl-optimizer,zeux/glsl-optimizer,dellis1972/glsl-optimizer,wolf96/glsl-optimizer,jbarczak/glsl-optimizer,wolf96/glsl-optimizer,tokyovigilante/glsl-optimizer,bkaradzic/glsl-optimizer,benaadams/glsl-optimizer,mapbox/glsl-optimizer,zeux/glsl-optimizer,tokyovigilante/glsl-optimizer,dellis1972/glsl-optimizer,metora/MesaGLSLCompiler,mcanthony/glsl-optimizer,zz85/glsl-optimizer,dellis1972/glsl-optimizer,zz85/glsl-optimizer,zz85/glsl-optimizer,mapbox/glsl-optimizer,djreep81/glsl-optimizer,zz85/glsl-optimizer,tokyovigilante/glsl-optimizer,dellis1972/glsl-optimizer,mcanthony/glsl-optimizer,bkaradzic/glsl-optimizer,bkaradzic/glsl-optimizer,benaadams/glsl-optimizer,djreep81/glsl-optimizer,bkaradzic/glsl-optimizer,mcanthony/glsl-optimizer,dellis1972/glsl-optimizer,jbarczak/glsl-optimizer,mapbox/glsl-optimizer,zeux/glsl-optimizer,bkaradzic/glsl-optimizer,tokyovigilante/glsl-optimizer,zz85/glsl-optimizer,mcanthony/glsl-optimizer,mapbox/glsl-optimizer,metora/MesaGLSLCompiler,benaadams/glsl-optimizer,djreep81/glsl-optimizer