pcmcia: make pcmcia_release_io() void, as no-one is interested in return value

As the only user of pcmcia_release_io() is not interested in its return
value, and we cannot do anything on failure, convert the function to return
void.

Reported-by: Jason Wang <wangborong@cdjrlc.com>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>