rtl8xxxu: fix uninitialized return value in ret

rtl8xxxu: fix uninitialized return value in ret

several functions are not initializing a return status in ret
resulting in garbage to be returned instead of 0 for success.
Currently, the calls to these functions are not checking the
return, however, it seems prudent to return the correct status
in case they are to be checked at a later date.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>