Fix a typo in a comment in the arm cpu_loop code.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Warner Losh <imp@bsdimp.com>
Message-Id: <20220114182535.3804783-1-peter.maydell@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>