powerpc: kernel/kgdb.c: Fix memory leakage

the variable backup_current_thread_info isn't freed before existing the
function.
Signed-off-by: Cong Ding <dinggnu@gmail.com>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/kernel/kgdb.c

@@ -154,12 +154,12 @@ static int kgdb_handle_breakpoint(struct pt_regs *regs)
 static int kgdb_singlestep(struct pt_regs *regs)
 {
 	struct thread_info *thread_info, *exception_thread_info;
-	struct thread_info *backup_current_thread_info = \
-		(struct thread_info *)kmalloc(sizeof(struct thread_info), GFP_KERNEL);
+	struct thread_info *backup_current_thread_info;
 
 	if (user_mode(regs))
 		return 0;
 
+	backup_current_thread_info = (struct thread_info *)kmalloc(sizeof(struct thread_info), GFP_KERNEL);
 	/*
 	 * On Book E and perhaps other processors, singlestep is handled on
 	 * the critical exception stack.  This causes current_thread_info()
@@ -185,6 +185,7 @@ static int kgdb_singlestep(struct pt_regs *regs)
 		/* Restore current_thread_info lastly. */
 		memcpy(exception_thread_info, backup_current_thread_info, sizeof *thread_info);
 
+	kfree(backup_current_thread_info);
 	return 1;
 }