rtw88: remove unnecessary variable

The variable ret is defined at the beginning and initialized
to 0 until the function returns ret, and the variable ret is
not reassigned.Therefore, we do not need to define the variable
ret, just return 0 directly at the end of the function.

Signed-off-by: wengjianfeng <wengjianfeng@yulong.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20210223075438.13676-1-samirweng1979@163.com