lora/sx126x: Clean up some struct formatting.

Changes are cosmetic - and maybe very minor code size - but not functional.
_reg_read() was calling struct.packinto() with an incorrect number of
arguments but it seems like Micropython didn't mind, as result is correct
for both versions.

This work was funded through GitHub Sponsors.

Signed-off-by: Angus Gratton <angus@redyak.com.au>

Author: projectgus

micropython/lora/lora-sx126x/lora/sx126x.py

@@ -469,7 +469,7 @@ def calibrate(self):
         # See DS 13.1.12 Calibrate Function
 
         # calibParam 0xFE means to calibrate all blocks.
-        self._cmd("<BB", _CMD_CALIBRATE, 0xFE)
+        self._cmd("BB", _CMD_CALIBRATE, 0xFE)
 
         time.sleep_us(_CALIBRATE_TYPICAL_TIME_US)
 
@@ -545,7 +545,7 @@ def start_recv(self, timeout_ms=None, continuous=False, rx_length=0xFF):
         else:
             timeout = 0  # Single receive mode, no timeout
 
-        self._cmd(">BBH", _CMD_SET_RX, timeout >> 16, timeout)
+        self._cmd(">BBH", _CMD_SET_RX, timeout >> 16, timeout)  # 24 bits
 
         return self._dio1
 
@@ -729,10 +729,10 @@ def _cmd(self, fmt, *write_args, n_read=0, write_buf=None, read_buf=None):
             return res
 
     def _reg_read(self, addr):
-        return self._cmd("BBBB", _CMD_READ_REGISTER, addr >> 8, addr & 0xFF, n_read=1)[0]
+        return self._cmd(">BHB", _CMD_READ_REGISTER, addr, 0, n_read=1)[0]
 
     def _reg_write(self, addr, val):
-        return self._cmd("BBBB", _CMD_WRITE_REGISTER, addr >> 8, addr & 0xFF, val & 0xFF)
+        return self._cmd(">BHB", _CMD_WRITE_REGISTER, addr, val & 0xFF)
 
 
 class _SX1262(_SX126x):