staging: wilc1000: remove static variable 'del_beacon' and null check

Using local variable instead of static varible 'del_beacon'. Also removed
the unnecessary 'if' check in handle_del_beacon().

Signed-off-by: Ajay Singh <ajay.kathat@microchip.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>