KVM: Fix include dependency for mmu_notifier

The kvm_host struct can include an mmu_notifier struct but mmu_notifier.h is
not included directly.
Signed-off-by: NEric B Munson <emunson@mgebm.net>
Signed-off-by: NAvi Kivity <avi@redhat.com>

include/linux/kvm_host.h

@@ -14,6 +14,7 @@
 #include <linux/signal.h>
 #include <linux/sched.h>
 #include <linux/mm.h>
+#include <linux/mmu_notifier.h>
 #include <linux/preempt.h>
 #include <linux/msi.h>
 #include <linux/slab.h>