Reduce RK steps in swerve mpc

We had more steps than needed, and it was causing expensive iterations.
This saves like 30% of the runtime.

Change-Id: Ic41f40b3e545bdce121b3c77036a2dddfea69273
Signed-off-by: Austin Schuh <austin.linux@gmail.com>
diff --git a/frc971/control_loops/swerve/casadi_velocity_mpc.py b/frc971/control_loops/swerve/casadi_velocity_mpc.py
index fc4a4c6..d108931 100644
--- a/frc971/control_loops/swerve/casadi_velocity_mpc.py
+++ b/frc971/control_loops/swerve/casadi_velocity_mpc.py
@@ -176,7 +176,7 @@
         U = casadi.MX.sym('U', 8)
 
         X = X0
-        M = 4  # RK4 steps per interval
+        M = 2  # RK4 steps per interval
         DT = self.dt / M
 
         for j in range(M):