panfrost: Leave push_constants pointer to NULL if there's no uniform

This removes a warning in pandecode.

Signed-off-by: Boris Brezillon <boris.brezillon@collabora.com>
Reviewed-by: Alyssa Rosenzweig <alyssa.rosenzweig@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/7408>
diff --git a/src/gallium/drivers/panfrost/pan_cmdstream.c b/src/gallium/drivers/panfrost/pan_cmdstream.c
index 36ee00d..ce55bce 100644
--- a/src/gallium/drivers/panfrost/pan_cmdstream.c
+++ b/src/gallium/drivers/panfrost/pan_cmdstream.c
@@ -936,7 +936,8 @@
                 }
         }
 
-        *push_constants = transfer.gpu;
+        if (ss->uniform_count)
+                *push_constants = transfer.gpu;
 
         buf->dirty_mask = 0;
         return ubos.gpu;