Add missing header to make it build (related to #1534577)

openssh-7.6p1-audit.patch

@@ -85,7 +85,7 @@ diff -up openssh-7.6p1/audit.c.audit openssh-7.6p1/audit.c
  
  #ifdef SSH_AUDIT_EVENTS
  
-@@ -34,6 +35,11 @@
+@@ -34,6 +35,12 @@
  #include "key.h"
  #include "hostfile.h"
  #include "auth.h"
@@ -94,6 +94,7 @@ diff -up openssh-7.6p1/audit.c.audit openssh-7.6p1/audit.c
 +#include "xmalloc.h"
 +#include "misc.h"
 +#include "servconf.h"
++#include "ssherr.h"
  
  /*
   * Care must be taken when using this since it WILL NOT be initialized when