spi: lpspi: fix dataloss when SS is inactivated between every words

If we don't use CONT to keep SS activated or use DMA mode without
cs-gpio, SS will be inactivated between every words. The word here
means the data sent once which length can be set as 1/2/4 bytes.

In the isr function, we read the FSR_RXCOUNT just behind the
fsl_lpspi_read_rx_fifo. This causes the value of FSR_RXCOUNT cannot
reflect whether there is still data not sent timely. So do this
judgement by FSR_TXCOUNT.
Signed-off-by: Clark Wang <xiaoning.wang@nxp.com>
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-fsl-lpspi.c

@@ -62,7 +62,7 @@
 #define CFGR1_PCSPOL	BIT(8)
 #define CFGR1_NOSTALL	BIT(3)
 #define CFGR1_MASTER	BIT(0)
-#define FSR_RXCOUNT	(BIT(16)|BIT(17)|BIT(18))
+#define FSR_TXCOUNT	(0xFF)
 #define RSR_RXEMPTY	BIT(1)
 #define TCR_CPOL	BIT(31)
 #define TCR_CPHA	BIT(30)
@@ -452,7 +452,7 @@ static irqreturn_t fsl_lpspi_isr(int irq, void *dev_id)
 	}
 
 	if (temp_SR & SR_MBF ||
-	    readl(fsl_lpspi->base + IMX7ULP_FSR) & FSR_RXCOUNT) {
+	    readl(fsl_lpspi->base + IMX7ULP_FSR) & FSR_TXCOUNT) {
 		writel(SR_FCF, fsl_lpspi->base + IMX7ULP_SR);
 		fsl_lpspi_intctrl(fsl_lpspi, IER_FCIE);
 		return IRQ_HANDLED;