[ELF] - Refactor readCallGraph().
[ELF] - Refactor readCallGraph().

This simplifies the code a bit.

It is NFC except that it removes early exit for Count == 0
which does not seem to be useful (we have no such tests either).

Differential revision: https://reviews.llvm.org/D49136

git-svn-id: f6089bf0e6284f307027cef4f64114ee9ebb0424@338953 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/lld,llvm-mirror/lld