soundwire: disable runtime PM before marking it as suspend

Before runtime PM is marked as suspended for the device, runtime
PM should be suspended for synchronization purpose. Without this,
the RPM status might not be updated to suspended and system might
go out of sync.

Change-Id: I77ce240bfae338f47d38277e115869a11df18101
Signed-off-by: Banajit Goswami <bgoswami@codeaurora.org>