max_map_count: corrected max_map_count condition

* kernel test for max_map_count_sysctl is:
   /* Too many mappings? */
   if (mm->map_count > sysctl_max_map_count)
     return -ENOMEM;
  so in LTP test map_count should be greater than max_map_count by 1

* only [vsyscall] is allocated without incrementing mm->map_count

Author: Bob Picco <bob.picco@oracle.com>

Signed-off-by: Stanislav kholmanskikh <stanislav.kholmanskikh@oracle.com>
Acked-by: Caspar Zhang <caspar@casparzhang.com>
Reviewed-by: Zhouping Liu <zliu@redhat.com>
Signed-off-by: Wanlong Gao <gaowanlong@cn.fujitsu.com>