I2C: omap: Fix error condition when slave sends a NAK

Fix an issue in the omap i2c host controller driver where it was not properly
clearing out an error condition in the unit after a NAK'ed transaction causing
the subsequent transaction to time out.

Change-Id: I5cdc8e740acdbc8116dca4d13f1a2cee37f75582
Signed-off-by: Mike J. Chen <mjchen@google.com>
Signed-off-by: Ruslan Bilovol <ruslan.bilovol@ti.com>