KVM: fix sparse warning

Impact: make global function static

  virt/kvm/kvm_main.c:85:6: warning: symbol 'kvm_rebooting' was not declared. Should it be static?
Signed-off-by: Hannes Eder <hannes@hanneseder.net>
Signed-off-by: Avi Kivity <avi@redhat.com>

virt/kvm/kvm_main.c

@@ -82,7 +82,7 @@ struct dentry *kvm_debugfs_dir;
 static long kvm_vcpu_ioctl(struct file *file, unsigned int ioctl,
 			   unsigned long arg);
 
-bool kvm_rebooting;
+static bool kvm_rebooting;
 
 #ifdef KVM_CAP_DEVICE_ASSIGNMENT