msm: mdss: Fix ARGC error when writing LUT to registers

When updating the ARGC LUT registers, the data is incorrectly written
such that the arrays are off by one index. This patch fixes that error
by starting from the correct index.

Also, when the READ flag is enabled for ARGC, the dirty flag is no longer
set.

Change-Id: I7e8e19c51d5891cd11344a425f1a8ac47d57368c
Signed-off-by: Benet Clark <benetc@codeaurora.org>