x86: fix compile error with corruption checking disabled

Fix compile error:

 arch/x86/mm/init_32.c: In function 'mem_init':
 arch/x86/mm/init_32.c:908: error: implicit declaration of function 'start_periodic_check_for_corruption'
Signed-off-by: NJeremy Fitzhardinge <jeremy.fitzhardinge@citrix.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

include/linux/kernel.h

@@ -251,6 +251,10 @@ void start_periodic_check_for_corruption(void);
 static inline void check_for_bios_corruption(void)
 {
 }
+
+static inline void start_periodic_check_for_corruption(void)
+{
+}
 #endif
 
 /* Values used for system_state */