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

commit 86b3bde0 upstream.

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/spi/spi-bcm63xx.c

@@ -180,8 +180,6 @@ 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 */