wlcore: add space for private area when allocating fw_status

When allocating the fw_status structure, the space for the
lower-driver private area was missing.  This was causing an illegal
write outside the allocated area, which was causing random oopses
around the kernel.

Signed-off-by: Luciano Coelho <coelho@ti.com>
Signed-off-by: Arik Nemtsov <arik@wizery.com>