hostap_80211.h: remove duplicate prototype

There were two identical prototypes for hostap_80211_rx() in
drivers/net/wireless/hostap/hostap_80211.h.

This patch fixes kernel Bugzilla #8930.

Reported by Christoph Burger-Scheidlin.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>