docs: x86: replace do_IRQ int the entry_64.rst with common_interrupt()

do_IRQ has been replaced by common_interrupt in commit
fa5e5c40

 ("x86/entry: Use idtentry for interrupts").

Signed-off-by: Tuo Cao <91tuocao@gmail.com>
Link: https://lore.kernel.org/r/20220915150155.9908-1-91tuocao@gmail.com
Signed-off-by: Jonathan Corbet <corbet@lwn.net>