firmware: microchip: fail auto-update probe if no flash found

There's no point letting the driver probe if there is no flash, as
trying to do a firmware upload will fail. Move the code that attempts
to get the flash from firmware upload to probe, and let it emit a
message to users stating why auto-update is not supported.
The code currently could have a problem if there's a flash in
devicetree, but the system controller driver fails to get a pointer to
it from the mtd subsystem, which will cause
mpfs_sys_controller_get_flash() to return an error. Check for errors and
null, instead of just null, in the new clause.

CC: stable@vger.kernel.org
Fixes: ec5b0f1 ("firmware: microchip: add PolarFire SoC Auto Update support")
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>

Author: ConchuOD

drivers/firmware/microchip/mpfs-auto-update.c

@@ -113,10 +113,6 @@ static enum fw_upload_err mpfs_auto_update_prepare(struct fw_upload *fw_uploader
 	 * be added here.
 	 */
 
-	priv->flash = mpfs_sys_controller_get_flash(priv->sys_controller);
-	if (!priv->flash)
-		return FW_UPLOAD_ERR_HW_ERROR;
-
 	erase_size = round_up(erase_size, (u64)priv->flash->erasesize);
 
 	/*
@@ -427,6 +423,12 @@ static int mpfs_auto_update_probe(struct platform_device *pdev)
 		return dev_err_probe(dev, PTR_ERR(priv->sys_controller),
 				     "Could not register as a sub device of the system controller\n");
 
+	priv->flash = mpfs_sys_controller_get_flash(priv->sys_controller);
+	if (IS_ERR_OR_NULL(priv->flash)) {
+		dev_dbg(dev, "No flash connected to the system controller, auto-update not supported\n");
+		return -ENODEV;
+	}
+
 	priv->dev = dev;
 	platform_set_drvdata(pdev, priv);