update mxs-dma filter function to firstly filter the dma channels only for
mxs-dma, rather than checking unrelated dma chans in following code.

Signed-off-by: Han Xu <han.xu@nxp.com>
(cherry picked from commit c0f60c87e5af4d8dddb81055fb6ce1477a615de0)
(Vipul: Fixed merge conflicts)
Signed-off-by: Vipul Kumar <vipul_kumar@mentor.com>
Signed-off-by: Srikanth Krishnakar <Srikanth_Krishnakar@mentor.com>