wpa_passphrase: Include $(LIBS) for linking

wpa_passphrase: Include $(LIBS) for linking

wpa_passphrase requires libcrypto from OpenSSL (or another selected
library). User can set an alternative path to OpenSSL libraries by
defining LIBS at the top of .config but if $(LIBS) is not actually used
wrong libcrypto is used or compilation fails if there is no libcrypto in
the default locations cc is looking for it. It's especially bad for
cross-compilers that fail with 'cannot find -lcrypto' message.

Signed-off-by: Arkadiusz Drabczyk <arkadiusz@drabczyk.org>