Don't rely on indirect inclusion of machine/bus.h to use

bus_space_{read,write}_* routines.  This doesn't matter in the current
tree, but will matter soon (the rest of the tree appears to already be
clean).

sys/dev/cpufreq/ichss.c

@@ -38,6 +38,7 @@ __FBSDID("$FreeBSD$");
 #include <sys/systm.h>
 
 #include <dev/pci/pcivar.h>
+#include <machine/bus.h>
 #include <machine/clock.h>
 #include <machine/resource.h>
 #include <sys/rman.h>