Update test/partial_idct_test.cc
Update test/partial_idct_test.cc

Makes more sense to call the corresponding partial idct C function
instead of the full idct C function as the reference.

Change-Id: Ibb7681dd063edd6307ba582c10c26c4c6a4b78c6

webmproject/libvpx,ShiftMediaProject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx,webmproject/libvpx,webmproject/libvpx,ShiftMediaProject/libvpx