arm_mptimer: Don't use hw_error() in realize() method

Device realize() methods aren't supposed to call hw_error(), they
should set an error and fail cleanly.  Do that.

Cc: Peter Maydell <peter.maydell@linaro.org>
Cc: qemu-arm@nongnu.org
Signed-off-by: NMarkus Armbruster <armbru@redhat.com>
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Message-Id: <1450370121-5768-4-git-send-email-armbru@redhat.com>

hw/timer/arm_mptimer.c

@@ -220,8 +220,9 @@ static void arm_mptimer_realize(DeviceState *dev, Error **errp)
     int i;
 
     if (s->num_cpu < 1 || s->num_cpu > ARM_MPTIMER_MAX_CPUS) {
-        hw_error("%s: num-cpu must be between 1 and %d\n",
-                 __func__, ARM_MPTIMER_MAX_CPUS);
+        error_setg(errp, "num-cpu must be between 1 and %d",
+                   ARM_MPTIMER_MAX_CPUS);
+        return;
     }
     /* We implement one timer block per CPU, and expose multiple MMIO regions:
      *  * region 0 is "timer for this core"