x86 setup: correct segfault in generation of 32-bit reloc kernel

Impact: segfault on build of a 32-bit relocatable kernel

When converting arch/x86/boot/compressed/relocs.c to support unlimited
sections, the computation of sym_strtab in walk_relocs() was done
incorrectly.  This causes a segfault for some people when building the
relocatable 32-bit kernel.

Pointed out by Anonymous <pageexec@freemail.hu>.
Signed-off-by: H. Peter Anvin <hpa@zytor.com>

arch/x86/boot/compressed/relocs.c

@@ -492,7 +492,7 @@ static void walk_relocs(void (*visit)(Elf32_Rel *rel, Elf32_Sym *sym))
 			continue;
 		}
 		sh_symtab = sec_symtab->symtab;
-		sym_strtab = sec->link->strtab;
+		sym_strtab = sec_symtab->link->strtab;
 		for (j = 0; j < sec->shdr.sh_size/sizeof(Elf32_Rel); j++) {
 			Elf32_Rel *rel;
 			Elf32_Sym *sym;