dma: mxs-dma: Always leave mxs_dma_init() with the clock disabled.

There is no need to have the clock enabled all the time the driver is
loaded.
It will be enabled anyway in mxs_dma_alloc_chan_resources() when a
channel is actually going to be used.

Signed-off-by: Lothar Waßmann <LW@KARO-electronics.de>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>