Flag is __maybe_unused, not __maybe_used.

Cc: Federico Vaga <federico.vaga@vaga.pv.it>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: linux-doc@vger.kernel.org
Cc: clang-built-linux@googlegroups.com
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Link: https://lore.kernel.org/r/20200715122328.3882187-1-lee.jones@linaro.orgSigned-off-by: Jonathan Corbet <corbet@lwn.net>