system: watchdog_set: fix misleading indentation

Fixes error reported by clang version 10.0.0-+20200102091410:

 system.c:367:4: error: misleading indentation; statement is not part of the previous 'if' [-Werror,-Wmisleading-indentation]
                  watchdog_timeout(timeout);
                  ^
 system.c:365:3: note: previous statement is here
                 if (timeout <= frequency)

Signed-off-by: Petr Štetiar <ynezz@true.cz>