platform/x86: asus_wmi: Fix return value of fan_boost_mode_store

Function fan_boost_mode_store returns 0 if store is successful,
this leads to infinite loop after any write to it's sysfs entry:

# echo 0 >/sys/devices/platform/asus-nb-wmi/fan_boost_mode

This command never ends, one CPU core is at 100% utilization.
This patch fixes this by returning size of written data.

Fixes: b096f626 ("platform/x86: asus-wmi: Switch fan boost mode")
Signed-off-by: Leonid Maksymchuk <leonmaxx@gmail.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/platform/x86/asus-wmi.c

@@ -1722,7 +1722,7 @@ static ssize_t fan_boost_mode_store(struct device *dev,
 	asus->fan_boost_mode = new_mode;
 	fan_boost_mode_write(asus);
 
-	return result;
+	return count;
 }
 
 // Fan boost mode: 0 - normal, 1 - overboost, 2 - silent