dma: dw: improve comparison with ~0

In general ~0 does not fit some integer types. Let's do a helper to make a
comparison with that constant properly.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>