[S390] Fix linker script.

6360b1fb ("move BUG_TABLE into RODATA")
causes this build bug (binutils 2.18.50.0.8.20080709, gcc 4.3.1):

  AS      .tmp_kallsyms1.o
  LD      .tmp_vmlinux2
  KSYM    .tmp_kallsyms2.S
s390x-4.3.1-nm: .tmp_vmlinux2: File truncated
No valid symbol.
make: *** [.tmp_kallsyms2.S] Error 1

So fix this.

Cc: Jan Beulich <jbeulich@novell.com>
Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>