misc-fix: unify updates of some probabilities

This commit merge the fix that unify the probability updates for UV
intra modes and partitions.

Related tracking issue:
https://bugs.chromium.org/p/webm/issues/detail?id=1040
point#5
Original libvpx commit:
d8f3bb1837f7ef966b1a380359e84d15bb92e18b

Change-Id: I892383a64916364cca42d8725ad05e87bf56de90