mods/machspi.c: Fix the bug in spi.read()

Mentioned here: https://forum.pycom.io/topic/1260/spi-bug
The parameter write=.. in spi.read() was ignored. Instead always
0x55 was sent.
This is a fix of the previous commit, which was wrong

Author: robert-hh

esp32/mods/machspi.c

@@ -195,10 +195,14 @@ STATIC void pybspi_transfer (mach_spi_obj_t *self, const char *txdata, char *rxd
     for (int i = 0; i < len; i += self->wlen) {
         uint32_t _rxdata = 0;
         uint32_t _txdata;
-        if (txchar) {
-            _txdata = *txchar;
+        if (txdata) {
+            memcpy(&_txdata, &txdata[i], self->wlen);
         } else {
-            _txdata = 0x55555555;
+            if (txchar) {
+                _txdata = *txchar;
+            } else {
+                _txdata = 0x55555555;
+            }
         }
         spi_data_t spidata = {.cmd = 0, .cmdLen = 0, .addr = NULL, .addrLen = 0,
                                 .txData = &_txdata, .txDataLen = self->wlen,