wl3501_cs: remove redundant variable rc

The variable rc is being initialized with a value that is never
read and it is being updated later with a new value that is returned.
The variable is redundant and can be replaced with a return 0 as
there are no other return points in this function.

Addresses-Coverity: ("Unused value")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>