drivers: spi: mcux_flexcomm: fix invalid dma config for last tx packets.

fixes an incorrect dma configuration. When lpc dma driver was extended
with gather/scatter support the spi dma driver stopped working.

(cherry picked from commit 79a2e24)

Original-Signed-off-by: Johan Carlsson <johan.carlsson@teenage.engineering>
GitOrigin-RevId: 79a2e24
Change-Id: I78227abb37328ce00b13a96e486a8b2dcf6e6e0f
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/zephyr/+/5666211
Reviewed-by: Ting Shen <phoenixshen@chromium.org>
Commit-Queue: Ting Shen <phoenixshen@chromium.org>
Tested-by: ChromeOS Prod (Robot) <chromeos-ci-prod@chromeos-bot.iam.gserviceaccount.com>
Tested-by: Ting Shen <phoenixshen@chromium.org>

drivers/spi/spi_mcux_flexcomm.c

@@ -400,7 +400,6 @@ static int spi_mcux_dma_tx_load(const struct device *dev, const uint8_t *buf,
  if (last_packet &&
  ((word_size > 8) ? (len > 2U) : (len > 1U))) {
  spi_mcux_prepare_txdummy(&data->last_word, last_packet, spi_cfg);
- blk_cfg->source_gather_en = 1;
  blk_cfg->source_address = (uint32_t)&data->dummy_tx_buffer;
  blk_cfg->dest_address = (uint32_t)&base->FIFOWR;
  blk_cfg->block_size = (word_size > 8) ?
@@ -434,7 +433,6 @@ static int spi_mcux_dma_tx_load(const struct device *dev, const uint8_t *buf,
  */
  if (last_packet &&
  ((word_size > 8) ? (len > 2U) : (len > 1U))) {
- blk_cfg->source_gather_en = 1;
  blk_cfg->source_address = (uint32_t)buf;
  blk_cfg->dest_address = (uint32_t)&base->FIFOWR;
  blk_cfg->block_size = (word_size > 8) ?