infiniband/ulp/ipoib: remove pkey_mutex

The last user of pkey_mutex was removed in db84f880 ("IB/ipoib: Use
P_Key change event instead of P_Key polling mechanism") but the lock
remained.
This patch removes it.
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Bart Van Assche <bart.vanassche@sandisk.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>

drivers/infiniband/ulp/ipoib/ipoib_ib.c

@@ -51,8 +51,6 @@ MODULE_PARM_DESC(data_debug_level,
 		 "Enable data path debug tracing if > 0");
 #endif
 
-static DEFINE_MUTEX(pkey_mutex);
-
 struct ipoib_ah *ipoib_create_ah(struct net_device *dev,
 				 struct ib_pd *pd, struct ib_ah_attr *attr)
 {