gallium/util: Increase the debug_flush map depth to 64

Piglit tests fbo-generatemipmap-3d RGB9_E5 and
fbo-generatemipmap-cubemap array RGB9_E5 hit assert when debug_flush
is active. Increase the debug map depth to 64.

Reviewed-by: Neha Bhende <bhenden@vmware.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/16061>

src/gallium/auxiliary/util/u_debug_flush.c

@@ -51,7 +51,7 @@
 #include <stdio.h>
 
 /* Future improvement: Use realloc instead? */
-#define DEBUG_FLUSH_MAP_DEPTH 32
+#define DEBUG_FLUSH_MAP_DEPTH 64
 
 struct debug_map_item {
    struct debug_stack_frame *frame;