wl12xx: send testmode reply in wl1271_tm_cmd_interrogate

wl1271_tm_cmd_interrogate creates a reply skb, but doesn't
send it (and thus just leaks it).
Add the missing cfg80211_testmode_reply() call.

Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>