ARM: dts: msm: Limit USB3 maximum speed to high for MSM8996 ADP

Owing to multiple compliance and functional issues reported on
MSM8996 ADP, limit USB3 maximum speed to high until the issues
are sorted out.

Change-Id: Ie7c28efcb86488b3b1bd0149d35b07979a14c171
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>