i2c: Fill req_seq in i2c_post_bind()

For i2c controllers which are missing alias in DT there is no req_seq
setup. This function is setting up proper ID based on highest found
alias ID.

On zcu102 this is the behavior when patch is applied.
ZynqMP> i2c bus
Bus 0:	i2c@ff020000
   20: gpio@20, offset len 1, flags 0
   21: gpio@21, offset len 1, flags 0
   75: i2c-mux@75, offset len 1, flags 0
Bus 2:	i2c@0
Bus 3:	i2c@1
Bus 4:	i2c@2
Bus 1:	i2c@ff030000  (active 1)
   74: i2c-mux@74, offset len 1, flags 0
   75: i2c-mux@75, offset len 1, flags 0
Bus 5:	i2c@0  (active 5)
   54: eeprom@54, offset len 1, flags 0
Bus 6:	i2c@1
Bus 7:	i2c@2
Bus 8:	i2c@3
Bus 9:	i2c@4
Bus 10:	i2c@0
Bus 11:	i2c@1
Bus 12:	i2c@2
Bus 13:	i2c@3
Bus 14:	i2c@4
Bus 15:	i2c@5
Bus 16:	i2c@6
Bus 17:	i2c@7

Before this patch applied (controllers have -1 ID)
ZynqMP> i2c bus
Bus 0:	i2c@ff020000
   20: gpio@20, offset len 1, flags 0
   21: gpio@21, offset len 1, flags 0
   75: i2c-mux@75, offset len 1, flags 0
Bus -1:	i2c@0
Bus -1:	i2c@1
Bus -1:	i2c@2
Bus 1:	i2c@ff030000  (active 1)
   74: i2c-mux@74, offset len 1, flags 0
   75: i2c-mux@75, offset len 1, flags 0
Bus -1:	i2c@0  (active 0)
   54: eeprom@54, offset len 1, flags 0
Bus -1:	i2c@1
Bus -1:	i2c@2
Bus -1:	i2c@3
Bus -1:	i2c@4
Bus -1:	i2c@0
Bus -1:	i2c@1
Bus -1:	i2c@2
Bus -1:	i2c@3
Bus -1:	i2c@4
Bus -1:	i2c@5
Bus -1:	i2c@6
Bus -1:	i2c@7

Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Heiko Schocher <hs@denx.de>
diff --git a/drivers/i2c/i2c-uclass.c b/drivers/i2c/i2c-uclass.c
index 7595b9b..49e23a0 100644
--- a/drivers/i2c/i2c-uclass.c
+++ b/drivers/i2c/i2c-uclass.c
@@ -623,6 +623,30 @@
 	int max_id;
 };
 
+static int i2c_post_bind(struct udevice *dev)
+{
+	struct uclass *class = dev->uclass;
+	struct i2c_priv *priv = class->priv;
+	int ret = 0;
+
+	/* Just for sure */
+	if (!priv)
+		return -ENOMEM;
+
+	debug("%s: %s, req_seq=%d\n", __func__, dev->name, dev->req_seq);
+
+	/* if there is no alias ID, use the first free */
+	if (dev->req_seq == -1)
+		dev->req_seq = ++priv->max_id;
+
+	debug("%s: %s, new req_seq=%d\n", __func__, dev->name, dev->req_seq);
+
+#if CONFIG_IS_ENABLED(OF_CONTROL) && !CONFIG_IS_ENABLED(OF_PLATDATA)
+	ret = dm_scan_fdt_dev(dev);
+#endif
+	return ret;
+}
+
 int i2c_uclass_init(struct uclass *class)
 {
 	struct i2c_priv *priv = class->priv;
@@ -647,9 +671,7 @@
 	.id		= UCLASS_I2C,
 	.name		= "i2c",
 	.flags		= DM_UC_FLAG_SEQ_ALIAS,
-#if CONFIG_IS_ENABLED(OF_CONTROL) && !CONFIG_IS_ENABLED(OF_PLATDATA)
-	.post_bind	= dm_scan_fdt_dev,
-#endif
+	.post_bind	= i2c_post_bind,
 	.init		= i2c_uclass_init,
 	.priv_auto_alloc_size = sizeof(struct i2c_priv),
 	.post_probe	= i2c_post_probe,