Re-lock the ath lock after ath_reset() has been called.

The calibrate callout is done with the sc lock held.

This only showed up when using an older NIC (AR5212) whose
radio/phy requires the rfgain adjustment.

Pointy-hat-to:	adrian
Sponsored by:	Hobnob, Inc.

sys/dev/ath/if_ath.c

@@ -5370,6 +5370,7 @@ ath_calibrate(void *arg)
 			sc->sc_doresetcal = AH_TRUE;
 			ATH_UNLOCK(sc);
 			ath_reset(ifp, ATH_RESET_NOLOSS);
+			ATH_LOCK(sc);
 			return;
 		}
 		/*