i2c-cpm: Detect and report NAK right away instead of timing out

Make the driver report an ENXIO error immediately upon NAK instead of
waiting for another interrupt and getting a timeout.

When reading from a device that is not present or declines to respond
to, e.g., a non-existent register address, CPM immediately reports a
NAK condition in the TxBD, but the driver kept waiting until a timeout,
which takes 1 second and causes an ugly console error message.

Signed-off-by: Mike Ditto <mditto@consentry.com>
Acked-by: Jochen Friedrich <jochen@scram.de>
[ben-linux@fluff.org: reordered description text]
Signed-off-by: Ben Dooks <ben-linux@fluff.org>