wcn36xx: drop unnecessary initialization of variables

Initialization is unneccessary when the variable is written before it is
read. There were some occasions in which the driver would initialize `ret'
during declaration without need.

Purely a cosmetic change with no functional impact.

Signed-off-by: Daniel Mack <daniel@zonque.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>