Documentation/locking/locktypes: fix local_locks documentation

Fix issues with local_locks documentation:
- fix function names, local_lock.h has local_unlock_irqrestore(),
not local_lock_irqrestore()
- fix mapping table, local_unlock_irqrestore() maps to local_irq_restore(),
not _save()

Signed-off-by: Marta Rybczynska <rybczynska@gmail.com>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lore.kernel.org/r/CAApg2=SKxQ3Sqwj6TZnV-0x0cKLXFKDaPvXT4N15MPDMKq724g@mail.gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>