drm/panel: sitronix-st7789v: Use 9 bits per spi word by default

The Sitronix controller expects 9-bit words, provide this as default at
probe time rather than specifying this in each and every access.

Signed-off-by: Miquel Raynal <miquel.raynal@bootlin.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Acked-by: Maxime Ripard <mripard@kernel.org>
Reviewed-by: Sebastian Reichel <sre@kernel.org>
Tested-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Sebastian Reichel <sre@kernel.org>
Signed-off-by: Neil Armstrong <neil.armstrong@linaro.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230714013756.1546769-17-sre@kernel.org

drivers/gpu/drm/panel/panel-sitronix-st7789v.c

@@ -142,7 +142,6 @@ static int st7789v_spi_write(struct st7789v *ctx, enum st7789v_prefix prefix,
 	u16 txbuf = ((prefix & 1) << 8) | data;
 
 	xfer.tx_buf = &txbuf;
-	xfer.bits_per_word = 9;
 	xfer.len = sizeof(txbuf);
 
 	return spi_sync_transfer(ctx->spi, &xfer, 1);
@@ -436,6 +435,11 @@ static int st7789v_probe(struct spi_device *spi)
 	spi_set_drvdata(spi, ctx);
 	ctx->spi = spi;
 
+	spi->bits_per_word = 9;
+	ret = spi_setup(spi);
+	if (ret < 0)
+		return dev_err_probe(&spi->dev, ret, "Failed to setup spi\n");
+
 	ctx->info = device_get_match_data(&spi->dev);
 
 	drm_panel_init(&ctx->panel, dev, &st7789v_drm_funcs,