i2c: davinci: fixup wait_for_completion_timeout handling

wait_for_completion_timeout return 0 (timeout) or >=1 (completion) so the check
for >= 0 is always true and can be dropped implying that r==-EREMOTEIO and thus
the return of -EREMOTEIO can be done in the   if (dev->buf_len)  branch.
As wait_for_completion_timeout returns unsigned long not int, and   int r   is
exclusively used for wait_for_completion_timeout it is renamed and the type
changed to unsigned long.

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Acked-by: Alexander Sverdlin <alexander.sverdlin@nokia.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>