spi_mpc83xx: hang fix

When the spi_mpc83xx driver receives a tx_buf pointer which is NULL, it
only writes one zero filled word to the transmit register.  If the driver
expects to receive more than one word it will wait forever for a second
receive interrupt.  With this patch the controller will shift out zeroes
until all words have been received.
Signed-off-by: NJan Andersson <jan@gaisler.com>
Tested-by: NAnton Vorontsov <avorontsov@ru.mvista.com>
Signed-off-by: NDavid Brownell <dbrownell@users.sourceforge.net>
Acked-by: NKumar Gala <galak@kernel.crashing.org>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/spi/spi_mpc83xx.c

@@ -384,11 +384,8 @@ irqreturn_t mpc83xx_spi_irq(s32 irq, void *context_data)
 
 	mpc83xx_spi->count -= 1;
 	if (mpc83xx_spi->count) {
-		if (mpc83xx_spi->tx) {
 		u32 word = mpc83xx_spi->get_tx(mpc83xx_spi);
-			mpc83xx_spi_write_reg(&mpc83xx_spi->base->transmit,
-					      word);
-		}
+		mpc83xx_spi_write_reg(&mpc83xx_spi->base->transmit, word);
 	} else {
 		complete(&mpc83xx_spi->done);
 	}