Documentation: core-api: packing: correct spelling

Correct spelling problems for Documentation/core-api/packing.rst as
reported by codespell.

Signed-off-by: Randy Dunlap <rdunlap@infradead.org>
Cc: Vladimir Oltean <olteanv@gmail.com>
Cc: Jonathan Corbet <corbet@lwn.net>
Reviewed-by: Mukesh Ojha <quic_mojha@quicinc.com>
Acked-by: Daniel Jordan <daniel.m.jordan@oracle.com>
Link: https://lore.kernel.org/r/20230215053738.11562-1-rdunlap@infradead.org


Signed-off-by: Jakub Kicinski <kuba@kernel.org>