powerpc/ptrace: Fix brk.len used uninitialised

With some CONFIGS it's possible that in ppc_set_hwdebug, brk.len is
uninitialised before being used.  It has been reported that GCC 4.2 will
produce the following error in this case:

  arch/powerpc/kernel/ptrace.c:1479: warning: 'brk.len' is used uninitialized in this function
  arch/powerpc/kernel/ptrace.c:1381: note: 'brk.len' was declared here

This patch corrects this.
Signed-off-by: Michael Neuling <mikey@neuling.org>
Reported-by: Philippe De Muyter <phdm@macqel.be>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/ptrace.c

@@ -1428,6 +1428,7 @@ static long ppc_set_hwdebug(struct task_struct *child,
 
 	brk.address = bp_info->addr & ~7UL;
 	brk.type = HW_BRK_TYPE_TRANSLATE;
+	brk.len = 8;
 	if (bp_info->trigger_type & PPC_BREAKPOINT_TRIGGER_READ)
 		brk.type |= HW_BRK_TYPE_READ;
 	if (bp_info->trigger_type & PPC_BREAKPOINT_TRIGGER_WRITE)