spi/bcm63xx: don't substract prepend length from total length

The spi command must include the full message length including any
prepended writes, else transfers larger than 256 bytes will be
incomplete.

Signed-off-by: Jonas Gorski <jogo@openwrt.org>
Acked-by: Florian Fainelli <florian@openwrt.org>
Signed-off-by: Mark Brown <broonie@linaro.org>
Cc: stable@vger.kernel.org

drivers/spi/spi-bcm63xx.c

@@ -169,8 +169,6 @@ static int bcm63xx_txrx_bufs(struct spi_device *spi, struct spi_transfer *first,
 			       transfer_list);
 	}
 
-	len -= prepend_len;
-
 	init_completion(&bs->done);
 
 	/* Fill in the Message control register */