i2c-algo-bit: Always send a stop condition before leaving

The i2c-algo-bit driver doesn't behave well on read errors: it'll
bail out without even sending a stop condition on the bus, so the bus
will be stuck. So make sure that we always send a stop condition on
the bus before we leave. The best way to make sure is to always send
it at the end of function bit_xfer.

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