dmaengine: dmatest: Prevent to run on misconfigured channel

dmaengine: dmatest: Prevent to run on misconfigured channel

Andy reported that commit 68abfaa37834 ("dmaengine: dmatest:
Restore default for channel") broke his scripts for the case
where "busy" channel is used for configuration with expectation
that run command would do nothing. Instead, behavior was
(unintentionally) changed to treat such case as under-configuration
and progress with defaults, i.e. run command would start a test
with default setting for channel (which would use all channels).

Restore original behavior with tracking status of channel setter
so we can distinguish between misconfigured and under-configured
cases in run command and act accordingly.

Fixes: 68abfaa37834 ("dmaengine: dmatest: Restore default for channel")
Reported-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Vladimir Murzin <vladimir.murzin@arm.com>
Tested-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/r/20200922115847.30100-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Vinod Koul <vkoul@kernel.org>