[WATCHDOG] Fix COH 901 327 watchdog enablement

Since the COH 901 327 found in U300 is clocked at 32 kHz we need
to wait for the interrupt clearing flag to propagate through
hardware in order not to accidentally fire off any interrupts
when we enable them.

Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Wim Van Sebroeck <wim@iguana.be>