dmaengine: fsldma: Unmap region obtained by of_iomap

Free memory mapping, if probe is not successful.

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Acked-by: Li Yang <leoyang.li@nxp.com>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>