[WATCHDOG] rm9k_wdt: fix compilation

Driver did not compile any more. Someone moved the definition
of 'struct miscdevice miscdev' to a place near the end of the
file, after some code that was refering to this variable.

Signed-off-by: Thomas Koeller <thomas.koeller@baslerweb.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>