mmc: sdhci-msm: Override DLL_CONFIG only if the valid value is supplied

mmc: sdhci-msm: Override DLL_CONFIG only if the valid value is supplied

During DLL initialization, the DLL_CONFIG register value would be
updated with the value supplied from the device-tree.

Override this register only if a valid value is supplied.

Fixes: 03591160ca19 ("mmc: sdhci-msm: Read and use DLL Config property from device tree file")
Signed-off-by: Veerabhadrarao Badiganti <vbadigan@codeaurora.org>
Link: https://lore.kernel.org/r/1594213888-2780-1-git-send-email-vbadigan@codeaurora.org
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>