Removed an unused local var from interpolate.cpp
Removed an unused local var from interpolate.cpp

Fixes a build warning from clang on OS X.

lookup1980/OpenSubdiv,c64kernal/OpenSubdiv,nyotis/OpenSubdiv,xldeveloper/OpenSubdiv,takahito-tejima/OpenSubdiv,nyotis/OpenSubdiv,shengfuintel/OpenSubdiv,nyotis/OpenSubdiv,poljere/OpenSubdiv,xldeveloper/OpenSubdiv,takahito-tejima/OpenSubdiv,c64kernal/OpenSubdiv,c64kernal/OpenSubdiv,takahito-tejima/OpenSubdiv,poljere/OpenSubdiv,shengfuintel/OpenSubdiv,lookup1980/OpenSubdiv,lookup1980/OpenSubdiv,poljere/OpenSubdiv,shengfuintel/OpenSubdiv,anshuarya/OpenSubdiv,anshuarya/OpenSubdiv,anshuarya/OpenSubdiv,xldeveloper/OpenSubdiv