Revert "i2c: bcm2835: Handle untimely DONE signal"

This reverts commit 431ac1d2.

Reverting this patch because it appears to have caused a regression
when used with an MPU-9250 IMU.

See: https://github.com/Hexxeh/rpi-firmware/issues/261



Signed-off-by: Phil Elwell <phil@raspberrypi.com>