ath10k: add some sanity checks to peer_map_event() functions

Smatch complains that since "ev->peer_id" comes from skb->data that
means we can't trust it and have to do a bounds check on it to prevent
an array overflow.

Fixes: 6942726f ('ath10k: add fast peer_map lookup')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Kalle Valo <kvalo@qca.qualcomm.com>