usb: musb: Update to use PM runtime autosuspend

Let's make the PM runtime use the standard autosuspend calls.
Commit 5de85b9d ("PM / runtime: Re-init runtime PM states at probe
error and driver unbind") means we must pair use_autosuspend with
dont_use_autosuspend and then use put_sync to properly idle the
device.

Note that we'll be removing the PM runtime calls from the glue
layer to the MUSB core in the next patch. And we can also remove
the pointless FIXME comment now.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>