glsl: Add missing bool case in glsl_type::get_scalar_type

Since the case was missing bec4->get_scalar_type() would return bvec4,
but vec4->get_scalar_type() would return float.

NOTE: This is a candidate for stable branches.

Signed-off-by: Ian Romanick <ian.d.romanick@intel.com>
Reviewed-by: Matt Turner <mattst88@gmail.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Jordan Justen <jordan.l.justen@intel.com>
(cherry picked from commit c770faea0a)

src/glsl/glsl_types.cpp

@@ -446,6 +446,8 @@ const glsl_type *glsl_type::get_scalar_type() const
       return int_type;
    case GLSL_TYPE_FLOAT:
       return float_type;
+   case GLSL_TYPE_BOOL:
+      return bool_type;
    default:
       /* Handle everything else */
       return type;