[elfabi] Fix the type of the variable formated for error output

Change the format type of Dyn.SONameOffset to PRIx64 since it is a uint64_t.
The problem was detected on mips builds, where it was printing junk values
and causing test failure.

Patch by Milos Stojanovic.

Differential Revision: https://reviews.llvm.org/D57676

llvm-svn: 353225