mmc: msm_sdcc: Fix possible circular locking dependency warning

In the context of request processing thread, data mover lock is
acquired after the host lock.  In another context, in the completion
handler of data mover the locks are acquired in the reverse order,
resulting in possible circular lock dependency warning. Hence,
schedule a tasklet to process the dma completion so as to avoid
nested locks.

Signed-off-by: Sahitya Tummala <stummala@codeaurora.org>
Signed-off-by: David Brown <davidb@codeaurora.org>