sfc: Remove some unreachable error paths

Some functions return an error code which is always 0.  Change their
return types to void and simplify their callers accordingly.

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: Jeff Garzik <jgarzik@redhat.com>
diff --git a/drivers/net/sfc/ethtool.c b/drivers/net/sfc/ethtool.c
index 906d18a..7989416 100644
--- a/drivers/net/sfc/ethtool.c
+++ b/drivers/net/sfc/ethtool.c
@@ -503,10 +503,10 @@
 	if (offline) {
 		/* Stop the kernel from sending packets during the test. */
 		efx_stop_queue(efx);
-		rc = efx_flush_queues(efx);
-		if (!rc)
-			rc = efx_offline_test(efx, &efx_tests,
-					      efx->loopback_modes);
+		efx_flush_queues(efx);
+
+		rc = efx_offline_test(efx, &efx_tests,
+				      efx->loopback_modes);
 		efx_wake_queue(efx);
 	}