brcmfmac: add missing break when deleting P2P_DEVICE

We obviously don't want to fall through in that switch. With this change
1) We wait for event (triggered by p2p_disc) as expected
2) We remove interface manually on timeout
3) We return 0 on success instead of -ENOTSUPP

Signed-off-by: Rafał Miłecki <zajec5@gmail.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>