rcu: undeclared variable used in documentation

The RCU documentation uses an fp variable which is not declared in the code
snippets. Use the new_fp variable instead.
Signed-Off-By: Baruch Even <baruch@ev-en.org>
Acked-by: <paulmck@us.ibm.com>
Signed-off-by: Adrian Bunk <bunk@stusta.de>

Documentation/RCU/whatisRCU.txt

@@ -360,7 +360,7 @@ uses of RCU may be found in listRCU.txt, arrayRCU.txt, and NMI-RCU.txt.
 		struct foo *new_fp;
 		struct foo *old_fp;
 
-		new_fp = kmalloc(sizeof(*fp), GFP_KERNEL);
+		new_fp = kmalloc(sizeof(*new_fp), GFP_KERNEL);
 		spin_lock(&foo_mutex);
 		old_fp = gbl_foo;
 		*new_fp = *old_fp;
@@ -461,7 +461,7 @@ The foo_update_a() function might then be written as follows:
 		struct foo *new_fp;
 		struct foo *old_fp;
 
-		new_fp = kmalloc(sizeof(*fp), GFP_KERNEL);
+		new_fp = kmalloc(sizeof(*new_fp), GFP_KERNEL);
 		spin_lock(&foo_mutex);
 		old_fp = gbl_foo;
 		*new_fp = *old_fp;