wireless: use ARRAY_SIZE

Using the ARRAY_SIZE macro improves the readability of the code. Also,
it is not always useful to use a variable to store this constant
calculated at compile time.

Found with Coccinelle with the following semantic patch:
@r depends on (org || report)@
type T;
T[] E;
position p;
@@
(
 (sizeof(E)@p /sizeof(*E))
|
 (sizeof(E)@p /sizeof(E[...]))
|
 (sizeof(E)@p /sizeof(T))
)

Signed-off-by: Jérémy Lefaure <jeremy.lefaure@lse.epita.fr>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>