docs: Fix the reference labels in Locking.rst

Note that you can also use :c:func:`spin_lock_irq()` or

:c:func:`spin_lock_irqsave()` here, which stop hardware interrupts

as well: see `Hard IRQ Context <#hardirq-context>`__.

as well: see `Hard IRQ Context <#hard-irq-context>`__.

This works perfectly for UP as well: the spin lock vanishes, and this

macro simply becomes :c:func:`local_bh_disable()`

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The same softirq can run on the other CPUs: you can use a per-CPU array

(see `Per-CPU Data <#per-cpu>`__) for better performance. If you're

(see `Per-CPU Data <#per-cpu-data>`__) for better performance. If you're

going so far as to use a softirq, you probably care about scalable

performance enough to justify the extra complexity.