input: Replace rcu_assign_pointer() with RCU_INIT_POINTER()

The use of "rcu_assign_pointer()" is NULLing out the pointer. According to RCU_INIT_POINTER()'s block comment:
"1. This use of RCU_INIT_POINTER() is NULLing out the pointer"
it is better to use it instead of rcu_assign_pointer() because it has a smaller overhead.

The following Coccinelle semantic patch was used:
@@
@@

- rcu_assign_pointer
+ RCU_INIT_POINTER
(..., NULL)

---
 drivers/input/input.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

index 1c4c0db..f9db5ea 100644
@@ -539,7 +539,7 @@ static void __input_release_device(struct input_handle *handle)
 	grabber = rcu_dereference_protected(dev->grab,
 					    lockdep_is_held(&dev->mutex));
 	if (grabber == handle) {
-		rcu_assign_pointer(dev->grab, NULL);
+		RCU_INIT_POINTER(dev->grab, NULL);
 		/* Make sure input_pass_event() notices that grab is gone */
 		synchronize_rcu();
 

1.9.1