i2c-mpc: Don't disable I2C module on stop condition

Disabling module on stop doesn't work on some CPUs (ie. mpc8241,
as reported by Guennadi Liakhovetski), so remove that.

Disable I2C module on errors/interrupts to prevent it from
locking up on mpc5200b.

Signed-off-by: Domen Puncer <domen.puncer@telargo.com>
Acked-by: Guennadi Liakhovetski <g.liakhovetski@gmx.de>
Signed-off-by: Jean Delvare <khali@linux-fr.org>