targets/nine: add note about fd owndership

v2:
 - move autotools hunk into correct patch
 - correct the note based on Axel's feedback

Cc: Axel Davy <axel.davy@ens.fr>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Acked-by: Rob Clark <robclark@freedesktop.org>

src/gallium/targets/d3dadapter9/drm.c

@@ -216,6 +216,8 @@ drm_create_adapter( int fd,
 
     ctx->base.destroy = drm_destroy;
 
+    /* Although the fd is provided from external source, mesa/nine
+     * takes ownership of it. */
     fd = loader_get_user_preferred_fd(fd, &different_device);
     ctx->fd = fd;
     ctx->base.linear_framebuffer = !!different_device;