While debugging a dma driver I noticed a memleak after
unloading the driver module.

Caught by kmemleak.
Signed-off-by: NAnatolij Gustschin <agust@denx.de>
Cc: Maciej Sosnowski <maciej.sosnowski@intel.com>
Signed-off-by: NDan Williams <dan.j.williams@intel.com>