staging: fieldbus: anybus-s: fix wait_for_completion_timeout return handling

wait_for_completion_timeout() returns unsigned long (0 on timeout or
remaining jiffies) not int. Assigning this return value to int may
theoretically overflow (though not in this case where TIMEOUT is
only HZ*2).

Fix this inconsistency by wrapping the wait_for_completion_timeout
into the if().

Signed-off-by: Nicholas Mc Guire <hofrat@osadl.org>
Reviewed-by: Sven Van Asbroeck <TheSven73@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>