smp_call_function_single(): be slightly less stupid, fix #2

fix m68k build failure:

 tip/kernel/up.c: In function 'smp_call_function_single':
 tip/kernel/up.c:16: error: dereferencing pointer to incomplete type
 make[2]: *** [kernel/up.o] Error 1
Signed-off-by: NIngo Molnar <mingo@elte.hu>

kernel/up.c

@@ -2,6 +2,7 @@
  * Uniprocessor-only support functions.  The counterpart to kernel/smp.c
  */
 
+#include <linux/interrupt.h>
 #include <linux/kernel.h>
 #include <linux/module.h>
 #include <linux/smp.h>