nir/linker: fix ARRAY_SIZE query with xfb varyings

For a non-array varying, it is expecting ARRAY_SIZE as 1, instead of 0.

Reviewed-by: Timothy Arceri <tarceri@itsqueeze.com>

src/compiler/glsl/gl_nir_link_xfb.c

       varying->Name = NULL;
       varying->Type = glsl_get_gl_type(xfb_varying->type);
       varying->BufferIndex = buffer_index;
-      varying->Size = glsl_get_length(xfb_varying->type);
+      varying->Size = glsl_type_is_array(xfb_varying->type) ?
+         glsl_get_length(xfb_varying->type) : 1;
       varying->Offset = xfb_varying->offset;
    }