fpga: of-fpga-region: accept overlays that don't program FPGA

The FPGA may already have a static image programmed when
Linux boots.  In that case a DT overlay may be used to add
the devices that already exist.  This commit allows that
by shuffling the order of some checks.
Signed-off-by: NAlan Tull <atull@kernel.org>
Acked-by: NMoritz Fischer <mdf@kernel.org>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/fpga/of-fpga-region.c

@@ -298,18 +298,19 @@ static int of_fpga_region_notify_pre_apply(struct fpga_region *region,
 	struct fpga_image_info *info;
 	int ret;
 
-	if (region->info) {
-		dev_err(dev, "Region already has overlay applied.\n");
-		return -EINVAL;
-	}
-
 	info = of_fpga_region_parse_ov(region, nd->overlay);
 	if (IS_ERR(info))
 		return PTR_ERR(info);
 
+	/* If overlay doesn't program the FPGA, accept it anyway. */
 	if (!info)
 		return 0;
 
+	if (region->info) {
+		dev_err(dev, "Region already has overlay applied.\n");
+		return -EINVAL;
+	}
+
 	region->info = info;
 	ret = fpga_region_program_fpga(region);
 	if (ret) {