usb: musb: Prepare dsps glue layer for PM runtime support

We want to be polling the state when nothing is connected.
Let's change the polling logic in preparation for PM runtime
support.

Signed-off-by: Tony Lindgren <tony@atomide.com>
[b-liu@ti.com: undo unnecessary line leading whitespace change]
Signed-off-by: Bin Liu <b-liu@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>