Doc-fix for PowerPC CPU model driver

There are some descriptions not right in PowerPC CPU model driver.
This patch is to fix them.
Signed-off-by: NLi Zhang <zhlcindy@linux.vnet.ibm.com>
Acked-by: NMichal Privoznik <mprivozn@redhat.com>

src/cpu/cpu_powerpc.c

 /*
- * cpu_powerpc.h: CPU driver for PowerPC CPUs
+ * cpu_powerpc.c: CPU driver for PowerPC CPUs
  *
- * Copyright (C) Copyright (C) IBM Corporation, 2010
+ * Copyright (C) IBM Corporation, 2010
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public