misc: minor fix for the gem5-SystemC/TLM coupling.

This patch has a minor fix for the coupling between gem5 and SystemC-TLM.

It also fixes some typos in the related documentation.

Change-Id: I894568729b8ebdacc5b81c9f46e8f9d137da210f
Reviewed-on: https://gem5-review.googlesource.com/2480
Reviewed-by: Jason Lowe-Power <jason@lowepower.com>
Maintainer: Jason Lowe-Power <jason@lowepower.com>