fsl_i2c: Wait for STOP condition to propagate

After issuing a STOP one must wait until the STOP has completed
on the bus before doing something new to the controller.

Also add an extra read of SR as the manual mentions doing that
is a good idea.

Remove surplus write of CR just before a write, isn't required and
could potentially disturb the I2C bus.

Signed-off-by: Joakim Tjernlund <Joakim.Tjernlund@transmode.se>