hostap: do not return positive number on failure path in prism2_open()

prism2_open() as an .ndo_open handler should not return positive numbers
in case of failure, but it does return 1 in a couple of places.

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

Signed-off-by: Alexey Khoroshilov <khoroshilov@ispras.ru>
Signed-off-by: John W. Linville <linville@tuxdriver.com>