asahi: Move assignment after null check.

Fix defect reported by Coverity Scan.

Dereference before null check (REVERSE_INULL)
check_after_deref: Null-checking so suggests that it may be null,
but it has already been dereferenced on all paths leading to the
check.

Fixes: dcd2d8ca50 ("asahi: Track more Gallium state")
Signed-off-by: Vinson Lee <vlee@freedesktop.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/11898>

src/gallium/drivers/asahi/agx_state.c

@@ -828,11 +828,12 @@ agx_create_shader_state(struct pipe_context *pctx,
                         const struct pipe_shader_state *cso)
 {
    struct agx_uncompiled_shader *so = CALLOC_STRUCT(agx_uncompiled_shader);
-   so->base = *cso;
 
    if (!so)
       return NULL;
 
+   so->base = *cso;
+
    if (cso->type == PIPE_SHADER_IR_NIR) {
       so->nir = cso->ir.nir;
    } else {