glsl2: Use gl_DepthRange's proper name.

It was being incorrectly added as gl_DepthRangeParameters, which is the
type name, not the variable name.
diff --git a/src/glsl/ir_variable.cpp b/src/glsl/ir_variable.cpp
index d9a16d4..d88cb51 100644
--- a/src/glsl/ir_variable.cpp
+++ b/src/glsl/ir_variable.cpp
@@ -141,7 +141,7 @@
 
    add_uniform(instructions, state, "gl_TextureMatrix", mat4_array_type);
 
-   add_uniform(instructions, state, "gl_DepthRangeParameters",
+   add_uniform(instructions, state, "gl_DepthRange",
 		state->symbols->get_type("gl_DepthRangeParameters"));
 
    add_uniform(instructions, state, "gl_ClipPlane",