systemc: Don't re-schedule a process which is already scheduled.

Change-Id: I8e12713c49aad03d0bfb779883adcbfa8fd4b42e
Reviewed-on: https://gem5-review.googlesource.com/c/13334
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>
3 files changed