uninit var in kpatch-elf.c

Initialize add_off earlier, so it's obviously never used uninitialized.
Clang was warning on this, even if gcc was not.
No functional change, the only path which left it undefined would call
ERROR() anyway.

kpatch-build/kpatch-elf.c

@@ -215,13 +215,12 @@ static void rela_insn(const struct section *sec, const struct rela *rela,
 long rela_target_offset(struct kpatch_elf *kelf, struct section *relasec,
 			struct rela *rela)
 {
-	long add_off;
+	long add_off = 0;
 	struct section *sec = relasec->base;
 
 	switch(kelf->arch) {
 	case AARCH64:
 	case PPC64:
-		add_off = 0;
 		break;
 	case X86_64:
 		if (!is_text_section(sec) ||