iwlegacy: remove redundant assignment to *res

Currently 1 is being assigned to *res and then it is immediately
updated with the computed result.  The first assignment is
redundant and can be removed.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Mukesh Ojha <mojha@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>