watchdog: diag288: Stop re-using watchdog core internal flags

A watchdog driver should not use watchdog subsystem internal flags.
Use a driver variable and flag instead to maintain the watchdog state
and to determine if a suspend operation is possible or not.

Signed-off-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>