wl12xx: Cleanup PLT mode when module is removed

PLT mode start/stop is controlled from userspace. When removing module, the
PLT mode state is however not checked, and not cleared. There is the possibility
of some unwanted state to left linger and there is even the possiblity of a
kernel crash if for instance IRQ work is running when the module is removed.

Fix this by stopping PLT mode on module removal, if still running.

Signed-off-by: Juuso Oikarinen <juuso.oikarinen@nokia.com>
Reviewed-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: Luciano Coelho <coelho@ti.com>