fvp: Remove unnecessary default case

The default case is impossible to hit as the `power_level`
is already checked earlier.  Avoids a clang warning.

Change-Id: I707463c843adc748ee9aa1d2313f9ab7dab3a8ab
Signed-off-by: dp-arm <dimitris.papastamos@arm.com>

plat/arm/board/fvp/fvp_pm.c

@@ -296,8 +296,6 @@ static int fvp_node_hw_state(u_register_t target_cpu,
 	case ARM_PWR_LVL1:
 		ret = (psysr & PSYSR_AFF_L1) ? HW_ON : HW_OFF;
 		break;
-	default:
-		assert(0);
 	}
 
 	return ret;