dmaengine: dmatest: Return boolean result directly in filter()

There is no need to have a conditional for boolean expression when
function returns bool. Drop unnecessary code and return boolean
result directly.

While at it, drop unneeded casting from void *.

Cc: Vladimir Murzin <vladimir.murzin@arm.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Tested-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Link: https://lore.kernel.org/r/20200922115847.30100-3-andriy.shevchenko@linux.intel.com


Signed-off-by: Vinod Koul <vkoul@kernel.org>