dw_dmac: use devm_* functions to simplify code

Use devm_kzalloc, devm_clk_get, devm_request_irq, and devm_request_and_ioremap
to reduce the code and to simplify the error path.

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