HAL_ChibiOS: fixed Hott telem half duplex handling

this fixes an issue with single byte writes with half duplex. It isn't
an elegent solution, but nicely separates the different types of half
duplex operation

libraries/AP_HAL_ChibiOS/UARTDriver.cpp

@@ -817,7 +817,7 @@ void UARTDriver::write_pending_bytes_NODMA(uint32_t n)
     ByteBuffer::IoVec vec[2];
     uint16_t nwritten = 0;
 
-    if (half_duplex) {
+    if (half_duplex && n > 1) {
         half_duplex_setup_tx();
     }