mtd: m25p80: consider max message size in m25p80_read

Consider a message size limit when calculating the maximum amount
of data that can be read.

The message size limit has been introduced with 4.9, so cc it
to stable.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Cyrille Pitchen <cyrille.pitchen@atmel.com>

drivers/mtd/devices/m25p80.c

@@ -172,7 +172,8 @@ static ssize_t m25p80_read(struct spi_nor *nor, loff_t from, size_t len,
 
 	t[1].rx_buf = buf;
 	t[1].rx_nbits = m25p80_rx_nbits(nor);
-	t[1].len = min(len, spi_max_transfer_size(spi));
+	t[1].len = min3(len, spi_max_transfer_size(spi),
+			spi_max_message_size(spi) - t[0].len);
 	spi_message_add_tail(&t[1], &m);
 
 	ret = spi_sync(spi, &m);