mtd: gpmi: only scan two chips for imx6

We cannot scan two chips for imx23 and imx28:
imx23: the Ready-Busy1 line is not connected for some board.
imx28: we do not set the pinctrl for Ready-Busy1

So we only scan two chips for imx6.

Signed-off-by: Huang Shijie <[e-mail]>
Signed-off-by: Brian Norris <[e-mail]>

drivers/mtd/nand/gpmi-nand/gpmi-nand.c

···
 	if (ret)
 		goto err_out;
 
-	ret = nand_scan_ident(mtd, 2, NULL);
+	ret = nand_scan_ident(mtd, GPMI_IS_MX6Q(this) ? 2 : 1, NULL);
 	if (ret)
 		goto err_out;