drm/msm/dsi: fix dsi command dma async race condition

Change will be removing checking and clearing dsi cmd done
interrupt in commit thread and in workqueue context, which
can race with dsi isr, when it tries to clear the interrupt.

Change-Id: I96e7f8dffed1af3cec0c7668ab1729337d4b260e
Signed-off-by: Vara Reddy <varar@codeaurora.org>