dma: cppi41: pass around device instead of platform_device

Instead of passing around struct plafform_device, use struct device and
save one level of dereferencing. This affects the following functions:

 * cppi41_add_chans
 * purge_descs
 * deinit_cpii41
 * init_descs
 * init_cppi41
 * cppi_glue_infos

It's just a cosmetic cleanup that makes the code more readable.

Signed-off-by: Daniel Mack <zonque@gmail.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>