eeepc-wmi: fix compiler warning

This fixes the following:

  CC [M]  drivers/platform/x86/eeepc-wmi.o
drivers/platform/x86/eeepc-wmi.c:322: warning: initialization from incompatible pointer type
Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
Signed-off-by: Matthew Garrett <mjg@redhat.com>

drivers/platform/x86/eeepc-wmi.c

@@ -298,8 +298,8 @@ static void eeepc_wmi_notify(u32 value, void *context)
 	kfree(obj);
 }
 
-static int store_cpufv(struct device *dev, struct device_attribute *attr,
-		       const char *buf, size_t count)
+static ssize_t store_cpufv(struct device *dev, struct device_attribute *attr,
+			   const char *buf, size_t count)
 {
 	int value;
 	struct acpi_buffer input = { (acpi_size)sizeof(value), &value };