wil6210: fix wil_cid_valid with negative cid values

There are several occasions where a negative cid value is passed
into wil_cid_valid and this is converted into a u8 causing the
range check of cid >= 0 to always succeed.  Fix this by making
the cid argument an int to handle any -ve error value of cid.

An example of this behaviour is in wil_cfg80211_dump_station,
where cid is assigned -ENOENT if the call to wil_find_cid_by_idx
fails, and this -ve value is passed to wil_cid_valid.  I believe
that the conversion of -ENOENT to the u8 value 254 which is
greater than wil->max_assoc_sta causes wil_find_cid_by_idx to
currently work fine, but I think is by luck and not the
intended behaviour.
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-by: Maya Erez <merez@codeaurora.org>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>

drivers/net/wireless/ath/wil6210/wil6210.h

@@ -1144,7 +1144,7 @@ static inline void wil_c(struct wil6210_priv *wil, u32 reg, u32 val)
 /**
  * wil_cid_valid - check cid is valid
  */
-static inline bool wil_cid_valid(struct wil6210_priv *wil, u8 cid)
+static inline bool wil_cid_valid(struct wil6210_priv *wil, int cid)
 {
 	return (cid >= 0 && cid < wil->max_assoc_sta);
 }