genetlink: Remove smp_read_barrier_depends() from comment

Now that smp_read_barrier_depends() has been de-emphasized, the less
said about it, the better.

Signed-off-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Kate Stewart <kstewart@linuxfoundation.org>
Cc: Ingo Molnar <mingo@kernel.org>
Cc: Philippe Ombredanne <pombredanne@nexb.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

include/linux/genetlink.h

@@ -31,8 +31,7 @@ extern wait_queue_head_t genl_sk_destructing_waitq;
  * @p: The pointer to read, prior to dereferencing
  *
  * Return the value of the specified RCU-protected pointer, but omit
- * both the smp_read_barrier_depends() and the READ_ONCE(), because
- * caller holds genl mutex.
+ * the READ_ONCE(), because caller holds genl mutex.
  */
 #define genl_dereference(p)					\
 	rcu_dereference_protected(p, lockdep_genl_is_held())