baum: Truncate braille device size to 84x1

Baum device bigger than 84 do not actually exist, but the user's own
Braille device might be wider than 84 columns.  Some guest drivers
would be upset by such sizes, so clamp the device size.
Signed-off-by: NSamuel Thibault <samuel.thibault@ens-lyon.org>
Message-Id: <20171211001950.27843-1-samuel.thibault@ens-lyon.org>
Signed-off-by: NPaolo Bonzini <pbonzini@redhat.com>

chardev/baum.c

 /*
  * QEMU Baum Braille Device
  *
- * Copyright (c) 2008, 2010-2011, 2016 Samuel Thibault
+ * Copyright (c) 2008, 2010-2011, 2016-2017 Samuel Thibault
  *
  * Permission is hereby granted, free of charge, to any person obtaining a copy
  * of this software and associated documentation files (the "Software"), to deal
@@ -239,6 +239,12 @@ static int baum_deferred_init(BaumChardev *baum)
         brlapi_perror("baum: brlapi__getDisplaySize");
         return 0;
     }
+    if (baum->y > 1) {
+        baum->y = 1;
+    }
+    if (baum->x > 84) {
+        baum->x = 84;
+    }
 
     con = qemu_console_lookup_by_index(0);
     if (con && qemu_console_is_graphic(con)) {