msm: mdss: fix OT limit configuration for WB1 module

Each VBIF client can be configured for its number of outstanding (OT)
transactions. Currently we can have as high as 13 of these VBIF clients
within MDP. OT configuration for these clients is spread across multiple
registers. Current implementation of rotator OT limit is not considering
these multiple registers which leads to incorrect OT limit configuration
for WB1 WR VBIF client. Fix this by adding logic to select correct
register offset.

Change-Id: I7b4f7ac37ff5c8a85f35dbeb6a6c450b157c4b3a
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>