IB/hfi1: Remove unused variable

The variable extended_psn was not used any more.
Signed-off-by: Kaike Wan <kaike.wan@intel.com>
Signed-off-by: Dennis Dalessandro <dennis.dalessandro@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@mellanox.com>

drivers/infiniband/hw/hfi1/user_sdma.h

 #ifndef _HFI1_USER_SDMA_H
 #define _HFI1_USER_SDMA_H
 /*
- * Copyright(c) 2015 - 2017 Intel Corporation.
+ * Copyright(c) 2015 - 2018 Intel Corporation.
  *
  * This file is provided under a dual BSD/GPLv2 license.  When using or
  * redistributing this file, you may do so under either license.
@@ -122,8 +122,6 @@ static inline int ahg_header_set(u32 *arr, int idx, size_t array_size,
 		 (req)->pq->ctxt, (req)->pq->subctxt, (req)->info.comp_idx, \
 		 ##__VA_ARGS__)
 
-extern uint extended_psn;
-
 struct hfi1_user_sdma_pkt_q {
 	u16 ctxt;
 	u16 subctxt;