arm64: fix typos in comments

Fix a typo "cortex"

Signed-off-by: Ken Kurematsu <k.kurematsu@nskint.co.jp>
Link: https://lore.kernel.org/r/OSBPR01MB3288B15006E15C64D4D617F7DBEF9@OSBPR01MB3288.jpnprd01.prod.outlook.com


Signed-off-by: Will Deacon <will@kernel.org>