sf: Read back and check once spansion quad bit set

One spansion quad bit set using CR, it's good to
read back and check the written bit and also if
it's already been set check for the bit and return.

Cc: Vignesh R <vigneshr@ti.com>
Cc: Simon Glass <sjg@chromium.org>
Cc: Bin Meng <bmeng.cn@gmail.com>
Cc: Michal Simek <michal.simek@xilinx.com>
Cc: Siva Durga Prasad Paladugu <sivadur@xilinx.com>
Tested-by: Mugunthan V N <mugunthanvnm@ti.com>
Signed-off-by: Jagan Teki <jteki@openedev.com>

drivers/mtd/spi/spi_flash.c

@@ -862,12 +862,18 @@ static int spansion_quad_enable(struct spi_flash *flash)
 	if (ret < 0)
 		return ret;
 
-	if (qeb_status & STATUS_QEB_WINSPAN) {
-		debug("SF: winspan: QEB is already set\n");
-	} else {
-		ret = write_cr(flash, STATUS_QEB_WINSPAN);
-		if (ret < 0)
-			return ret;
+	if (qeb_status & STATUS_QEB_WINSPAN)
+		return 0;
+
+	ret = write_cr(flash, STATUS_QEB_WINSPAN);
+	if (ret < 0)
+		return ret;
+
+	/* read CR and check it */
+	ret = read_cr(flash, &qeb_status);
+	if (!(ret >= 0 && (qeb_status & STATUS_QEB_WINSPAN))) {
+		printf("SF: Spansion CR Quad bit not clear\n");
+		return -EINVAL;
 	}
 
 	return ret;