wil6210: update unsigned type to signed type

wil_cid_valid can get cid type that is negative.
Change wil_cid_valid to get int instead of u8.

Change-Id: I8f46999db71bddbd60ebe5207ad56855ad5bf405
Signed-off-by: Alexei Avshalom Lazar <ailizaro@codeaurora.org>