powerpc/kexec: Fix up KEXEC_CONTROL_CODE_SIZE missed during conversion

powerpc/kexec: Fix up KEXEC_CONTROL_CODE_SIZE missed during conversion

Commit b45fa8191de3a3df56b2176a9969e225695e2b03 missed one, resulting in
the following compile error:

  AS      arch/powerpc/kernel/misc_32.o
arch/powerpc/kernel/misc_32.S: Assembler messages:
arch/powerpc/kernel/misc_32.S:902: Error: unsupported relocation against KEXEC_CONTROL_CODE_SIZE
make[2]: *** [arch/powerpc/kernel/misc_32.o] Error 1
make[1]: *** [arch/powerpc/kernel] Error 2
make: *** [vmlinux] Error 2

I grepped arch/ and found no further instances.

Signed-off-by: Paul Collins <paul@ondioline.org>
Signed-off-by: Paul Mackerras <paulus@samba.org>