msm: mdss: fix the stride value override issue in DMA

In the case of continuous splash the DMA initialization
happens in first COMMIT where the PREPARE call has already
updated the DMA parameters to the required values. Avoid
DMA initialization code resetting these values if the
PREPARE call has already updated them.

Change-Id: I97eab38d32fe09a6860fcf26377651f6c4815357
Signed-off-by: Shivaraj Shetty <shivaraj@codeaurora.org>