seqlock: Properly format kernel-doc code samples

Align the code samples and note sections inside kernel-doc comments with
tabs. This way they can be properly parsed and rendered by Sphinx. It
also makes the code samples easier to read from text editors.

Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lkml.kernel.org/r/20200720155530.1173732-3-a.darwish@linutronix.de