i2c-pxa.c: timeouts off by 1

With `while (timeout--)' timeout reaches -1 after the loop, so the tests
below are off by one.

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Acked-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Ben Dooks <ben-linux@fluff.org>