sim: Fix data type of ticks per second before passing it to C++

sim: Fix data type of ticks per second before passing it to C++

Casts ticks per second value to int before passing it to C++. Python
throws an error because of incompatible type because of the recent
change.

Change-Id: Ibcaf8c327f1be0dba38763975d389584addd8373
Reviewed-on: https://gem5-review.googlesource.com/c/14375
Reviewed-by: Gabe Black <gabeblack@google.com>
Maintainer: Gabe Black <gabeblack@google.com>