Eevee: Fix compilation error in eevee-next.

Although eevee-next is disabled in Blender 3.3 there is an error that is
visible when compiling shaders using the shader builder.

This is because of an error in a preprocessing directive (defined should
be define).

source/blender/draw/engines/eevee_next/shaders/eevee_attributes_lib.glsl

@@ -3,7 +3,7 @@
 #pragma BLENDER_REQUIRE(common_math_lib.glsl)
 #pragma BLENDER_REQUIRE(gpu_shader_codegen_lib.glsl)
 
-#defined EEVEE_ATTRIBUTE_LIB
+#define EEVEE_ATTRIBUTE_LIB
 
 #if defined(MAT_GEOM_MESH)