kbuild: fix dependency on sorttable

Commit ac4f0678 ("kbuild: Create intermediate vmlinux build with
relocations preserved") missed replacing one occurrence of "vmlinux"
that was added during the same development cycle.

Fixes: ac4f0678 ("kbuild: Create intermediate vmlinux build with relocations preserved")
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>
Acked-by: Ard Biesheuvel <ardb@kernel.org>