spi: dw-spi: Single Register read to clear IRQs

Instead of clearing the RxU, RxO, and TxO IRQs individually with
3 register reads, a single read of the ICR register will do the
same thing.

Signed-off-by: Thor Thayer <tthayer@opensource.altera.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-dw.c

@@ -232,9 +232,7 @@ static irqreturn_t interrupt_transfer(struct dw_spi *dws)
 
 	/* Error handling */
 	if (irq_status & (SPI_INT_TXOI | SPI_INT_RXOI | SPI_INT_RXUI)) {
-		dw_readw(dws, DW_SPI_TXOICR);
-		dw_readw(dws, DW_SPI_RXOICR);
-		dw_readw(dws, DW_SPI_RXUICR);
+		dw_readw(dws, DW_SPI_ICR);
 		int_error_stop(dws, "interrupt_transfer: fifo overrun/underrun");
 		return IRQ_HANDLED;
 	}