param MPC_MAN_TILT_MAX: decrease maximum from 90 to 85 degrees

At 90 degrees the yaw is extremely unstable (tested with HIL), it
overshoots and only very slowly converges to the correct value.
This behavior is also noticable with lower angles, but not so extreme.
It definitely needs to be looked into further, but for now this makes it
safer.

src/modules/mc_pos_control/mc_pos_control_params.c

@@ -341,7 +341,7 @@ PARAM_DEFINE_FLOAT(MPC_TKO_SPEED, 1.5f);
  *
  * @unit deg
  * @min 0.0
- * @max 90.0
+ * @max 85.0
  * @decimal 1
  * @group Multicopter Position Control
  */