carl9170: tx: Replace rcu_assign_pointer() with RCU_INIT_POINTER()

According to RCU_INIT_POINTER()'s block comment 3.a, it can be used if
"3.   The referenced data structure has already been exposed to readers either
at compile time or via rcu_assign_pointer() -and-
 a.   You have not made -any- reader-visible changes to this structure since
then".

This case fulfills the conditions above because between the rcu_dereference()
call (cvif = rcu_dereference(ar->beacon_iter);) and the rcu_assign_pointer()
call there is no update of the "cvif" variable.
Therefore, this patch makes the replacement.

The following Coccinelle semantic patch was used:
@@
identifier v;
@@

v = rcu_dereference(...);
... when != rcu_dereference(...);
    when != v = ...;
    when != (<+...v...+>)++;
    when != \(memcpy\|memset\)(...);
(
- rcu_assign_pointer
+ RCU_INIT_POINTER
  (..., v);
|
 if(...) {
... when != v = ...;
- rcu_assign_pointer
+ RCU_INIT_POINTER
  (..., v);
... when any
 }
)

Because there are cases where between a “rcu_dereference()” call and a
“rcu_assign_pointer()” call might be updates of the value that interests us,
the Coccinelle semantic patch ignores them and replaces with
"RCU_INIT_POINTER()" only when the update is not happening.
Signed-off-by: Andreea-Cristina Bernat <bernat.ada@gmail.com>
Acked-by: Christian Lamparter <chunkeey@googlemail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>

drivers/net/wireless/ath/carl9170/tx.c

@@ -1557,7 +1557,7 @@ static struct carl9170_vif_info *carl9170_pick_beaconing_vif(struct ar9170 *ar)
 	}
 
 out:
-	rcu_assign_pointer(ar->beacon_iter, cvif);
+	RCU_INIT_POINTER(ar->beacon_iter, cvif);
 	return cvif;
 }