freedreno/crashdec: Fix crash with older kernels

Older kernels lack the cluster-name property. Don't crash decoding
devcoredumps from them, even if they can't be converted to snapshots
properly.

Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/38931>

src/freedreno/decode/crashdec.c

@@ -257,7 +257,7 @@ debugbus_id(const char *name)
 static uint32_t
 cluster_id(const char *name)
 {
-   if (!is_a7xx())
+   if (!is_a7xx() || !name)
       return 0;
    return enumval("a7xx_cluster", name);
 }