[WATCHDOG] pcwd.c - fix open_allowed type.

Fix following warnings:
drivers/watchdog/pcwd.c: In function 'pcwd_open':
drivers/watchdog/pcwd.c:703: warning: passing argument 2 of 'test_and_set_bit' from incompatible pointer type
drivers/watchdog/pcwd.c: In function 'pcwd_close':
drivers/watchdog/pcwd.c:723: warning: passing argument 2 of 'clear_bit' from incompatible pointer type

Signed-off-by: Wim Van Sebroeck <wim@iguana.be>