disk_cache: assert if a cache entries keys don't match mesa

In ef42423e7be9 I enabled the check for release builds however we
still want to assert in debug builds in case of collisions or
just general bugs with the key building/compare code. Otherwise
it will just fail silently effectively disabling the cache.

Reviewed-by: Eduardo Lima Mitev <elima@igalia.com>
diff --git a/src/util/disk_cache.c b/src/util/disk_cache.c
index 36c1e8e..b789a45 100644
--- a/src/util/disk_cache.c
+++ b/src/util/disk_cache.c
@@ -1085,8 +1085,10 @@
       goto fail;
 
    /* Check for extremely unlikely hash collisions */
-   if (memcmp(cache->driver_keys_blob, file_header, ck_size) != 0)
+   if (memcmp(cache->driver_keys_blob, file_header, ck_size) != 0) {
+      assert(!"Mesa cache keys mismatch!");
       goto fail;
+   }
 
    size_t cache_item_md_size = sizeof(uint32_t);
    uint32_t md_type;