drm/msm/dsi-staging: check esd reg readback value correctly

Fix issue around checking esd register read back value with
the expected value from the dtsi entries.

Change-Id: I8aeccc3acb61f10c3141e42a15eb6c674af251e6
CRs-Fixed: 2183397
Signed-off-by: Vara Reddy <varar@codeaurora.org>