tmc2209: Set SENDDELAY=2 to avoid uart rx/tx errors

It looks like the tmc2209 chips have increased uart errors with the
default SENDDELAY of zero.  Increasing the SENDDELAY to two seems to
work around this issue.

Reported by @ReXT3D.

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

klippy/extras/tmc2209.py

@@ -59,6 +59,9 @@ class TMC2209:
         self.fields = tmc.FieldHelper(Fields, tmc2208.SignedFields,
                                       FieldFormatters)
         self.mcu_tmc = tmc_uart.MCU_TMC_uart(config, Registers, self.fields, 3)
+        # Setup fields for UART
+        self.fields.set_field("pdn_disable", True)
+        self.fields.set_field("SENDDELAY", 2) # Avoid tx errors on shared uart
         # Allow virtual pins to be created
         tmc.TMCVirtualPinHelper(config, self.mcu_tmc)
         # Register commands