wlcore: don't WARN_ON in case of existing ROC

When working with AP + P2P, it's possible to get into
a state when the AP is in ROC (due to assiciating station)
while trying to ROC on the P2P interface.

Replace the WARN_ON with wl1271_error to avoid warnings
in this case.

Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>