dw_spi: Fix missing final read in some polling situations

There is a possibility that the last word of a transaction will be lost
if data is not ready. Re-read in poll_transfer() to solve this issue
when poll_mode is enabled.

Verified on SPI touch screen device.

Signed-off-by: Major Lee <[e-mail]>
Signed-off-by: Alan Cox <[e-mail]>
Signed-off-by: Linus Torvalds <[e-mail]>

drivers/spi/dw_spi.c

···
 {
 	while (dws->write(dws))
 		dws->read(dws);
+	/*
+	 * There is a possibility that the last word of a transaction
+	 * will be lost if data is not ready. Re-read to solve this issue.
+	 */
+	dws->read(dws);
 
 	transfer_complete(dws);
 }