dw_dmac: move from __init to __devinit

We usually have more than one DMA device. Thus, the probe function should serve
for all of them in case when the driver is built as a module.

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