dma: mmp_pdma: add missing platform_set_drvdata() in mmp_pdma_probe()

Add missing platform_set_drvdata() in mmp_pdma_probe(), otherwise
calling platform_get_drvdata() in mmp_pdma_remove() returns NULL.

Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>