gallium/dri: Shut up a compiler warning.
gallium/dri: Shut up a compiler warning.

The compiler doesn't see that buffers is set in the !image case and used
in the !image case.

Reviewed-by: Matt Turner <789b315743a28dd066a4ba1459c35951c291d8a6@gmail.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler