i2c-algo-bit: Complain about masters which can't read SCL

The I2C specification explicitly describes both SDA and SCL as
bidirectional lines. An I2C master with a read-only SCL is thus not
compliant. If a slow slave stretches the clock, errors will happen,
so the bus can't be considered as reliable.

Signed-off-by: Jean Delvare <khali@linux-fr.org>