OMAP3: PM: fix IO daisy chain enable to use PM_WKEN reg

Checking to se if the IO daisy chain is enabled should be checking the
PM_WKEN register, not the PM_WKST register.  Reading PM_WKST tells us
if an event occurred, not whether or not it is enabled.

Apparently, we've been lucky until now in that a pending event has not
been there during enable.  However, on 3630/Zoom3, I noticed because
of the WARN that this timeout was always happening.

Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>