After commit 4d27e9dc (PM: Make power
domain callbacks take precedence over subsystem ones), the power
domain callbacks need to call the driver callbacks instead of relying
on the default subsystem (in this case, platform_bus) to handle the
driver callbacks.

Validated on 3430/n900, 3530/Overo.
Signed-off-by: Kevin Hilman <khilman@ti.com>