stats: Rename num_syscalls to numSyscalls in the reference stats.

stats: Rename num_syscalls to numSyscalls in the reference stats.

The name of the stat was changed in the following change which broke all the
reference outputs.

    commit 2367198921765848a4f5b3d020a7cc5776209f80
    Author: Brandon Potter <brandon.potter@amd.com>
    Date:   Mon Feb 27 14:10:15 2017 -0500

        syscall_emul: [PATCH 15/22] add clone/execve for threading and
        multiprocess simulations

Change-Id: Id98b085ccae098c50c434ad81a72beee46084f40
Reviewed-on: https://gem5-review.googlesource.com/2651
Maintainer: Jason Lowe-Power <jason@lowepower.com>
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>