kbuild: rename .tmp_vmlinux.kallsyms0.syms to .tmp_vmlinux0.syms

Change the naming for consistency.

While at this, fix the comments in scripts/link-vmlinux.sh.

Signed-off-by: Sedat Dilek <sedat.dilek@gmail.com>
Signed-off-by: Masahiro Yamada <masahiroy@kernel.org>