lenovo/t520/mainboard.c: Include header `h8.h` for prototype

Change-Id: I5ac6608ebf78f2d48bc7f68bce9eae7a2be82332
Signed-off-by: Elyes HAOUAS <ehaouas@noos.fr>
Reviewed-on: http://review.coreboot.org/6424
Tested-by: build bot (Jenkins)
Reviewed-by: Edward O'Callaghan <eocallaghan@alterapraxis.com>

src/mainboard/lenovo/t520/mainboard.c

@@ -39,6 +39,7 @@
 #include <device/pci.h>
 #include <cbfs.h>
 #include <pc80/keyboard.h>
+#include <ec/lenovo/h8/h8.h>
 
 void mainboard_suspend_resume(void)
 {
@@ -182,8 +183,6 @@ static void mainboard_enable(device_t dev)
 	verb_setup();
 }
 
-void h8_mainboard_init_dock (void);
-
 void h8_mainboard_init_dock (void)
 {
 	return;