Fix injecting data into a .o file

Use section.Offset instead of Addr.

Test: symbol_inject -i test.o -o test2.o -s symbol -v value
Change-Id: I9c54a5a245e7674b8370fc27ba7d0b9995f2ed08
diff --git a/cmd/symbol_inject/elf.go b/cmd/symbol_inject/elf.go
index 1741a5b..12253f6 100644
--- a/cmd/symbol_inject/elf.go
+++ b/cmd/symbol_inject/elf.go
@@ -56,7 +56,7 @@
 	case elf.ET_REL:
 		// "In relocatable files, st_value holds a section offset for a defined symbol.
 		// That is, st_value is an offset from the beginning of the section that st_shndx identifies."
-		return file.Sections[symbol.Section].Addr + symbol.Value, nil
+		return section.Offset + symbol.Value, nil
 	case elf.ET_EXEC, elf.ET_DYN:
 		// "In executable and shared object files, st_value holds a virtual address. To make these
 		// files’ symbols more useful for the dynamic linker, the section offset (file interpretation)