MLK-11325 dma: mxs-dma: fix dma_io clock enable count mismatch issue

After dma init by calling .mxs_dma_init(), disable dma_io and
dma_bch clocks. When dma chans are requested by devices, clocks
are enabled in .device_alloc_chan_resources(). The patch is to
fix clock enable count mismatch issue.

Signed-off-by: Fugang Duan <B38611@freescale.com>
(cherry picked from commit: 4868cf5e39a0aeb1ad12c5c1a453d233c0f472ce)