mmap: Fix memory leak when iterating over mapped memory

When returning from grub_mmap_iterate() the memory allocated to present
is not being released causing it to leak.

Fixes: CID 96655

Signed-off-by: Darren Kenny <darren.kenny@oracle.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

grub-core/mmap/mmap.c

@@ -270,6 +270,7 @@ grub_mmap_iterate (grub_memory_hook_t hook, void *hook_data)
 		   hook_data))
 	{
 	  grub_free (ctx.scanline_events);
+	  grub_free (present);
 	  return GRUB_ERR_NONE;
 	}
 
@@ -282,6 +283,7 @@ grub_mmap_iterate (grub_memory_hook_t hook, void *hook_data)
     }
 
   grub_free (ctx.scanline_events);
+  grub_free (present);
   return GRUB_ERR_NONE;
 }