I2C: OMAP: Don't check if wait_for_completion_timeout() returns less than zero

By definition, wait_for_completion_timeout() returns an unsigned value and
therefore, it is not necessary to check if the return value is less than zero
as this is not possible.

This is based on a patch from Jon Hunter <jon-hunter@ti.com>
Changes from his patch
- Declare a long as the wait_for_completion_timeout returns long.

Original patch is
http://git.omapzoom.org/?p=kernel/omap.git;a=commitdiff;h=ea02cece7b0000bc736e60c4188a11aaa74bc6e6

Reviewed-by: Kevin Hilman <khilman@ti.com>
Signed-off-by: Jon Hunter <jon-hunter@ti.com>
Signed-off-by: Shubhrajyoti D <shubhrajyoti@ti.com>
Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>