powerpc/rtas: Fix watchdog driver temperature read functionality

Using the RTAS watchdog driver to read out the temperature crashes
on a PXCAB:

Unable to handle kernel paging request for data at address 0xfe347b50
Faulting instruction address: 0xc00000000001af64
Oops: Kernel access of bad area, sig: 11 [#1]

The wrong usage of "(void *)__pa(&temperature)" in rtas_call() is
removed by using the function rtas_get_sensor() which does the
right thing.
Signed-off-by: NAdrian Reber <adrian@lisas.de>
Acked-by: NUtz Bacher <utz.bacher@de.ibm.com>
Signed-off-by: NBenjamin Herrenschmidt <benh@kernel.crashing.org>

drivers/watchdog/wdrtas.c

@@ -218,16 +218,14 @@ static void wdrtas_timer_keepalive(void)
  */
 static int wdrtas_get_temperature(void)
 {
-	long result;
+	int result;
 	int temperature = 0;
 
-	result = rtas_call(wdrtas_token_get_sensor_state, 2, 2,
-			   (void *)__pa(&temperature),
-			   WDRTAS_THERMAL_SENSOR, 0);
+	result = rtas_get_sensor(WDRTAS_THERMAL_SENSOR, 0, &temperature);
 
 	if (result < 0)
 		printk(KERN_WARNING "wdrtas: reading the thermal sensor "
-		       "faild: %li\n", result);
+		       "failed: %i\n", result);
 	else
 		temperature = ((temperature * 9) / 5) + 32; /* fahrenheit */