staging: wlags49_h2: fix error handling in pcmcia probe function

wl_adapter_attach() ignores some important issues
such as register_netdev() failure. The patch fixes it.

Found by Linux Driver Verification project (linuxtesting.org).

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>