mfd: pm8921: Update for genirq changes

Since this code has been marked broken for some time a few genirq
tree wide changes weren't made. set_irq_wake() was renamed to
irq_set_irq_wake() in commit a0cd9ca2 (genirq: Namespace
cleanup, 2011-02-10) and commit 10a8c383 (irq: introduce entry
and exit functions for chained handlers) introduced the chained
irq functions but this driver wasn't updated to use them. Fix
these problems and remove the BROKEN marking on this driver.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>