11-STABLE fails to build with MK_OFED enabled

[Pete French]

/usr/src/sys/modules/mlx4ib/../../ofed/drivers/infiniband/hw/mlx4/sysfs.c:90:22: error: 
      format specifies type 'unsigned long long *' but the argument has type
      'u64 *' (aka 'unsigned long *') [-Werror,-Wformat]
        sscanf(buf, "%llx", &sysadmin_ag_val);
                     ~~~~   ^~~~~~~~~~~~~~~~
                     %lx

Fairly trivial to fix obviously - I chnaged it to %lx - but not sure that would
work on non 64 bit platforms.

-pete.