i2c: xgene-slimpro: Fix missing mbox_free_channel call in probe error path

Free requested mailbox channel before return error.

Signed-off-by: Axel Lin <[e-mail]>
Signed-off-by: Wolfram Sang <[e-mail]>

drivers/i2c/busses/i2c-xgene-slimpro.c

···
 	rc = i2c_add_adapter(adapter);
 	if (rc) {
 		dev_err(&pdev->dev, "Adapter registeration failed\n");
+		mbox_free_channel(ctx->mbox_chan);
 		return rc;
 	}