Update comments and logging on return path for byte writes.  NAK is
an error, to be reported or optionally ignored.  Timeouts are always
errors.  Lost arbitration is not currently handled, so don't even list
it as an option in the error message.

Don't return bogus EFAULT code for inappropriate NAK; EIO is better,
there is no bad userspace address in question.
Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Signed-off-by: Jean Delvare <khali@linux-fr.org>