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>

drivers/i2c/busses/i2c-viapro.c

@@ -287,7 +287,7 @@ static s32 vt596_access(struct i2c_adapter *adap, u16 addr,
 	return 0;
 
 exit_unsupported:
-	dev_warn(&vt596_adapter.dev, "Unsupported command invoked! (0x%02x)\n",
+	dev_warn(&vt596_adapter.dev, "Unsupported transaction %d\n",
 		 size);
 	return -EOPNOTSUPP;
 }