llvm-objdump: fix remaining use of %x format specifier for 64-bit values

Third time lucky. This should finally fix the ARM (& MIPS, I think) bots.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@215349 91177308-0d34-0410-b5e6-96231b3b80d8