[Object] Fix missing arguments to getType and getSymbol in Elf_Rel_Impl

Somehow this was compiling without these methods having their arguments
passed to them. I used these methods in some code I wrote and it raised
an error on me. It appears no one else has used these methods let (LLD
uses setSymbolAndType however). This change resolves the issue.

Patch by Jake Ehrlich

Differential Revision: https://reviews.llvm.org/D35100

llvm-svn: 313336