brcmfmac: Remove sleep on del_station.

Currently there is a sleep after disconnect on del_station. This
timeout is not needed (anymore) and is causing problems with p2p
setup, because remote side disconnects then supplicant will do
del_station and while it waits the 400ms remote side will already
reconnect and that is something supplicant cant handle.

Reviewed-by: Arend Van Spriel <arend@broadcom.com>
Reviewed-by: Pieter-Paul Giesberts <pieterpg@broadcom.com>
Reviewed-by: Piotr Haber <phaber@broadcom.com>
Signed-off-by: Hante Meuleman <meuleman@broadcom.com>
Signed-off-by: Arend van Spriel <arend@broadcom.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>