ring-buffer: Fix bytes_dropped calculation issue

[ Upstream commit c73f0b69648501978e8b3e8fa7eef7f4197d0481 ]

The calculation of bytes-dropped and bytes_dropped_nested is reversed.
Although it does not affect the final calculation of total_dropped,
it should still be modified.

Link: https://lore.kernel.org/20250223070106.6781-1-yangfeng59949@163.com


Fixes: 6c43e554 ("ring-buffer: Add ring buffer startup selftest")
Signed-off-by: Feng Yang <yangfeng@kylinos.cn>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>