watchdog: hpwdt: fix unused variable warning

watchdog: hpwdt: fix unused variable warning

The new hpwdt_my_nmi() function is used conditionally, which produces
a harmless warning in some configurations:

drivers/watchdog/hpwdt.c:478:12: error: 'hpwdt_my_nmi' defined but not used [-Werror=unused-function]

This moves it inside of the #ifdef that protects its caller, to silence
the warning.

Fixes: 621174a92851 ("watchdog: hpwdt: Check source of NMI")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Jerry Hoemann <jerry.hoemann@hpe.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>