thermal: Fix compiler warning

The following warning is obtained when CONFIG_NET is not defined:

In file included from drivers/thermal/mvebu_thermal.c:27:0:
include/linux/thermal.h:254:12: warning: 'thermal_generate_netlink_event'
defined but not used [-Wunused-function]

This patch fixes the warning by properly inlining
thermal_generate_netlink_event().
Signed-off-by: NEzequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: NZhang Rui <rui.zhang@intel.com>

include/linux/thermal.h

@@ -251,7 +251,7 @@ void thermal_unregister_governor(struct thermal_governor *);
 extern int thermal_generate_netlink_event(struct thermal_zone_device *tz,
 						enum events event);
 #else
-static int thermal_generate_netlink_event(struct thermal_zone_device *tz,
+static inline int thermal_generate_netlink_event(struct thermal_zone_device *tz,
 						enum events event)
 {
 	return 0;