msm: mdss: remove dt documentation of an obsolete property

"qcom,mdss-high-ib-factor" property is obsolete and not required by the
driver. Remove it from the example documentation.

Change-Id: Id8b92ca4fc60d993494dfc9e7610f5f9f927eb64
Signed-off-by: Ujwal Patel <ujwalp@codeaurora.org>