glsl: Check for SSBO variable in check_for_ssbo_store
glsl: Check for SSBO variable in check_for_ssbo_store

The compiler probably already blocks this earlier on, but we should be
checking for an SSBO here.

Signed-off-by: Jordan Justen <a79006884ba9cf5f4f7fcbb92a15b208780d8c97@intel.com>
Reviewed-by: Iago Toral Quiroga <a847aabaac44184372f6b1cd1a59aa254daaeb0b@igalia.com>
Reviewed-by: Kristian Høgsberg <ca9b5b1e27d4fa7f4ba6848bdd08ca52cfd6330c@bitplanet.net>

metora/MesaGLSLCompiler,metora/MesaGLSLCompiler,metora/MesaGLSLCompiler