tracing: Fix unload_page for simple_ring_buffer init rollback

tracing: Fix unload_page for simple_ring_buffer init rollback

The unload_page callback expects the return value of load_page() as its
argument: ret = load_page(va); unload(ret). Fix the rollback code in
simple_ring_buffer_init_mm() where the descriptor's VA is used instead
of the loaded page address.

Link: https://patch.msgid.link/20260512141614.1759430-1-vdonnefort@google.com
Fixes: 635923081c79 ("tracing: load/unload page callbacks for simple_ring_buffer")
Signed-off-by: Vincent Donnefort <vdonnefort@google.com>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>