tmc: Fix order of init during sensorless homing

With commit 53b10d3a the setup of sensorless homing could occur before
the driver was enabled which would cause the reinitialization of the
driver settings to undo the sensorless homing setup.

Use set_field() when setting the sensorless homing registers so that
it wont conflict with a driver init.

Signed-off-by: Kevin O'Connor <kevin@koconnor.net>

klippy/extras/tmc5160.py

@@ -208,6 +208,9 @@ Fields["TPOWERDOWN"] = {
 Fields["TPWMTHRS"] = {
     "TPWMTHRS":                 0xfffff << 0
 }
+Fields["TCOOLTHRS"] = {
+    "TCOOLTHRS":                0xfffff << 0
+}
 Fields["TSTEP"] = {
     "TSTEP":                    0xfffff << 0
 }