rr_graph: Rename ch (channel) => t (track) variables
rr_graph: Rename ch (channel) => t (track) variables

Signed-off-by: John McMaster <527ca5438b47432dedda4309be2f991b71bfb11c@gmail.com>
Signed-off-by: Tim 'mithro' Ansell <b1c1d8736f20db3fb6c1c66bb1455ed43909f0d8@mith.ro>

SymbiFlow/symbiflow-arch-defs,SymbiFlow/symbiflow-arch-defs