PM / QoS: Fix default runtime_pm device resume latency

The recent change to the PM QoS framework to introduce a proper
no constraint value overlooked to handle the devices which don't
implement PM QoS OPS.  Runtime PM is one of the more severely
impacted subsystems, failing every attempt to runtime suspend
a device.  This leads into some nasty second level issues like
probe failures and increased power consumption among other
things.

Fix this by adding a proper return value for devices that don't
implement PM QoS.

Fixes: 0cc2b4e5

 (PM / QoS: Fix device resume latency PM QoS)
Signed-off-by: Tero Kristo <t-kristo@ti.com>
Cc: All applicable <stable@vger.kernel.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>