MAINTAINERS: Fix file pattern for MEN Z069 watchdog driver

The file name is menz69_wdt.c, not menz069_wdt.c.

Reported-by: Joe Perches <joe@perches.com>
Cc: Joe Perches <joe@perches.com>
Cc: Johannes Thumshirn <jth@kernel.org>
Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Wim Van Sebroeck <wim@linux-watchdog.org>
Signed-off-by: Wim Van Sebroeck <wim@linux-watchdog.org>