+ inline the function directly as there was only one consumer
(get_prob())

this is an attempt to reduce the amount of branches to workaround an amd
bug. this change is mildly faster or neutral across x86-64, arm.

http://support.amd.com/TechDocs/44739_12h_Rev_Gd.pdf
665 Integer Divide Instruction May Cause Unpredictable Behavior

cherry-picked from libvpx:
7481edb33 vpx_dsp/get_prob: make clip_prob branchless

Change-Id: I433059c61ce43ec5058cc16ca590d186bfa8aab5