i2c: Consistently reject unsupported transactions

Many PC SMBus host controller drivers don't properly handle the case
where they are requested to achieve a transaction they do not support.
Update them so that the consistently print a warning message and
return a single error value in this case.

Signed-off-by: Jean Delvare <khali@linux-fr.org>
diff --git a/drivers/i2c/busses/i2c-taos-evm.c b/drivers/i2c/busses/i2c-taos-evm.c
index de9db49..224aa12 100644
--- a/drivers/i2c/busses/i2c-taos-evm.c
+++ b/drivers/i2c/busses/i2c-taos-evm.c
@@ -96,9 +96,8 @@
 			sprintf(p, "$%02X", command);
 		break;
 	default:
-		dev_dbg(&adapter->dev, "Unsupported transaction size %d\n",
-			size);
-		return -EINVAL;
+		dev_warn(&adapter->dev, "Unsupported transaction %d\n", size);
+		return -EOPNOTSUPP;
 	}
 
 	/* Send the transaction to the TAOS EVM */