ARM: OMAP2+: devices: Fixes for McPDM

Commit f718e2c0 (ARM: OMAP2+: devices:
Remove all omap_device_pm_latency structures) removed these structures.
Commit 3528c58e

 (OMAP: omap_device:
when building return platform_device instead of omap_device) now
returns platform_device instead of omap_device.

Fix up the omap-mcpdm init function since this part comes via sound
tree, and there has been changes regarding to hwmod/omap_device_build.

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
CC: Benoit Cousson <b-cousson@ti.com>
CC: Kevin Hilman <khilman@ti.com>
[tony@atomide.com: updated comments]
Signed-off-by: Tony Lindgren <tony@atomide.com>