i2c-davinci: Fix signal handling bug

If wait_for_completion_interruptible_timeout exits due
to a signal, the i2c bus was locking up.

Signed-off-by: Troy Kisky <troy.kisky@boundarydevices.com>
Signed-off-by: Kevin Hilman <khilman@mvista.com>
Signed-off-by: Jean Delvare <khali@linux-fr.org>