brcmfmac: make non-global functions static

Fix sparse warning:
drivers/net/wireless/broadcom/brcm80211/brcmfmac/p2p.c:2206:5:
	warning: symbol 'brcmf_p2p_get_conn_idx' was not declared. Should it be static?
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Chen Zhou <chenzhou10@huawei.com>
Reviewed-by: Wright Feng <wright.feng@cypress.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Link: https://lore.kernel.org/r/20200508013249.95196-1-chenzhou10@huawei.com

drivers/net/wireless/broadcom/brcm80211/brcmfmac/p2p.c

@@ -2233,7 +2233,7 @@ static struct wireless_dev *brcmf_p2p_create_p2pdev(struct brcmf_p2p_info *p2p,
 	return ERR_PTR(err);
 }
 
-int brcmf_p2p_get_conn_idx(struct brcmf_cfg80211_info *cfg)
+static int brcmf_p2p_get_conn_idx(struct brcmf_cfg80211_info *cfg)
 {
 	int i;
 	struct brcmf_if *ifp = netdev_priv(cfg_to_ndev(cfg));