sfxge(4): add constant condition note to make lint happier

Found by lint on illumos.

Submitted by:   Garrett D'Amore <garrett at damore.org>
Sponsored by:   Solarflare Communications, Inc.
MFC after:      1 week

sys/dev/sfxge/common/ef10_mcdi.c

@@ -213,6 +213,7 @@ ef10_mcdi_poll_reboot(
 		 * this can be handled by common code drivers (and reworked to
 		 * support Siena too).
 		 */
+		_NOTE(CONSTANTCONDITION)
 		if (B_FALSE) {
 			rc = EIO;
 			goto fail1;

sys/dev/sfxge/common/ef10_nic.c

@@ -1677,6 +1677,7 @@ ef10_nic_register_test(
 
 	/* FIXME */
 	_NOTE(ARGUNUSED(enp))
+	_NOTE(CONSTANTCONDITION)
 	if (B_FALSE) {
 		rc = ENOTSUP;
 		goto fail1;

sys/dev/sfxge/common/ef10_tx.c

@@ -649,6 +649,7 @@ ef10_tx_qpace(
 
 	/* FIXME */
 	_NOTE(ARGUNUSED(etp, ns))
+	_NOTE(CONSTANTCONDITION)
 	if (B_FALSE) {
 		rc = ENOTSUP;
 		goto fail1;