I ran gdb to figure out the problem. I discovered that the length
of the quote is 52 bytes, and the header files in tss/tspi.h say the
offset within the quote at which the PCR composite hash appears is 49!
Thus 17 bytes of the hash are not in the quote. More investigation
allowed me to determine that the correct PCR composite hash starts at
offset 32. It's the last part of the quote, but the header files give
the wrong offset.