staging: wilc1000: correctly check if associatedsta has not been found

The current check for associatedsta being set to -1 to indicate it has
not been found is not working because associatedsta is initialized to
zero and will never be -1.  Fix this by initializing it to ~0 and checking
for ~0 instead.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>