glsl: don't incorrectly eliminate patches with explicit locations
glsl: don't incorrectly eliminate patches with explicit locations

These varying have a separate location domain from per-vertex varyings
and need to be handled separately.

Reviewed-by: Dave Airlie <f2295d84e358395675bc8031be58672073ae065e@redhat.com>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler