watchdog: ep93xx_wdt.c fix default timout value in MODULE_PARM_DESC string.

The WATCHDOG_TIMEOUT macro does not exist. The default timeout value is WDT_TIMEOUT.
Fix the MODULE_PARM_DESC so that the code can compile again.

reported-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>