IB/mthca: Free correct MPT on error exit from mthca_fmr_alloc()

When mthca_fmr_alloc() returns an error, it should free the MPT at the
index key, not mr->ibmr.lkey, since the lkey has been mangled by
hw_index_to_key() and no longer is the real index.  This bug causes
corruption of the MPT table free bitmap when mthca_fmr_alloc() fails.
Signed-off-by: Roland Dreier <rolandd@cisco.com>

drivers/infiniband/hw/mthca/mthca_mr.c

@@ -686,7 +686,7 @@ int mthca_fmr_alloc(struct mthca_dev *dev, u32 pd,
 	mthca_table_put(dev, dev->mr_table.mpt_table, key);
 
 err_out_mpt_free:
-	mthca_free(&dev->mr_table.mpt_alloc, mr->ibmr.lkey);
+	mthca_free(&dev->mr_table.mpt_alloc, key);
 	return err;
 }