gallium: properly propagate the usage of resource

In case that some drivers might make decision depending on it,
it is better to tell drivers about usage of resource just like
in `blit_to_staging()` and `st_TexSubImage()` etc before going
to blit.

Signed-off-by: Luc Ma <luc@sietium.com>
Reviewed-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/29833>

src/gallium/auxiliary/util/u_transfer_helper.c

@@ -194,6 +194,7 @@ transfer_map_msaa(struct pipe_context *pctx,
    if (!trans)
       return NULL;
    struct pipe_transfer *ptrans = &trans->base;
+   bool need_pack = needs_pack(usage);
 
    pipe_resource_reference(&ptrans->resource, prsc);
    ptrans->level = level;
@@ -207,6 +208,7 @@ transfer_map_msaa(struct pipe_context *pctx,
          .height0 = box->height,
          .depth0 = 1,
          .array_size = 1,
+         .usage = need_pack ? PIPE_USAGE_STAGING : 0,
    };
    if (util_format_is_depth_or_stencil(tmpl.format))
       tmpl.bind |= PIPE_BIND_DEPTH_STENCIL;
@@ -218,7 +220,7 @@ transfer_map_msaa(struct pipe_context *pctx,
       return NULL;
    }
 
-   if (needs_pack(usage)) {
+   if (need_pack) {
       struct pipe_blit_info blit;
       memset(&blit, 0, sizeof(blit));