iser-target: Fix error path in isert_create_pi_ctx()

We don't assign pi_ctx to desc->pi_ctx until we're certain to succeed
in the function.  That means the cleanup path should use the local
pi_ctx variable, not desc->pi_ctx.

This was detected by Coverity (CID 1260062).
Signed-off-by: Roland Dreier <roland@purestorage.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

drivers/infiniband/ulp/isert/ib_isert.c

@@ -547,11 +547,11 @@ isert_create_pi_ctx(struct fast_reg_descriptor *desc,
 	return 0;
 
 err_prot_mr:
-	ib_dereg_mr(desc->pi_ctx->prot_mr);
+	ib_dereg_mr(pi_ctx->prot_mr);
 err_prot_frpl:
-	ib_free_fast_reg_page_list(desc->pi_ctx->prot_frpl);
+	ib_free_fast_reg_page_list(pi_ctx->prot_frpl);
 err_pi_ctx:
-	kfree(desc->pi_ctx);
+	kfree(pi_ctx);
 
 	return ret;
 }