dmaengine: cppi41: Clean up pointless warnings

With patches "dmaengine: cppi41: Fix runtime PM timeouts with USB mass
storage", and "dmaengine: cppi41: Fix oops in cppi41_runtime_resume",
the pm_runtime_get/put() in cppi41_irq() is no longer needed. We now
guarantee that cppi41 is enabled when dma is in use.

We can still get pointless error -115 when musb is configured as a
usb peripheral. That's because we should now check for the state of
is_suspended instead.

Let's just remove the now useless code and replace it with a WARN().

Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>