Prefer common check_add_overflow() from overflow.h over the locally
rolled versions of it. While check_add_overflow() does require a
variable to assign to, unlike add_overflows_t(), it's still better than
having multiple versions around.

Cc: Kees Cook <keescook@chromium.org>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240405202625.2525671-1-jani.nikula@intel.comSigned-off-by: Jani Nikula <jani.nikula@intel.com>