Revert "drivers: spi: fix the update of spi_context tx & rx length"

This reverts commit 4a486ce.

This change was totally wrong.

Signed-off-by: Declan Snyder <declan.snyder@nxp.com>

Author: decsny

drivers/spi/spi_context.h

@@ -496,7 +496,7 @@ void spi_context_update_tx(struct spi_context *ctx, uint8_t dfs, uint32_t len)
 		return;
 	}
 
-	ctx->tx_len -= len * dfs;
+	ctx->tx_len -= len;
 	if (!ctx->tx_len) {
 		/* Current buffer is done. Get the next one to be processed. */
 		++ctx->current_tx;
@@ -555,7 +555,7 @@ void spi_context_update_rx(struct spi_context *ctx, uint8_t dfs, uint32_t len)
 		return;
 	}
 
-	ctx->rx_len -= len * dfs;
+	ctx->rx_len -= len;
 	if (!ctx->rx_len) {
 		/* Current buffer is done. Get the next one to be processed. */
 		++ctx->current_rx;