fix read for case (bits <= 32 && !wholeBytes) || len <= 4))

Before, each copy from SPI transaction buf to destination buf was overwriting
all previously copied data, so always only the last $bytesPerChunk bytes were
stored.
Fix by shifting pointer within destination buf to actually append newly read
data instead of overwriting.

ports/esp32/machine_hw_spi.c

@@ -274,6 +274,7 @@ STATIC void machine_hw_spi_transfer(mp_obj_base_t *self_in, size_t len, const ui
 
             if (dest != NULL) {
                 memcpy(dest, &transaction.rx_data, bytesPerChunk);
+                dest += bytesPerChunk;
             }
             src += bytesPerChunk;
             len -= bytesPerChunk;