mtd: m25p80: Revive dual read support

Commit 03e296f6 ("mtd: m25p80: use the SPI
nor framework") accidentally removed support for Dual SPI read transfers.
Add it back.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Huang Shijie <shijie8@gmail.com>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>

drivers/mtd/devices/m25p80.c

@@ -221,6 +221,8 @@ static int m25p_probe(struct spi_device *spi)
 
 	if (spi->mode & SPI_RX_QUAD)
 		mode = SPI_NOR_QUAD;
+	else if (spi->mode & SPI_RX_DUAL)
+		mode = SPI_NOR_DUAL;
 	ret = spi_nor_scan(nor, spi_get_device_id(spi), mode);
 	if (ret)
 		return ret;