pcmcia: fix unused function compile warning

pcmcia_socket_dev_resume() is only referenced from macro
SET_SYSTEM_SLEEP_PM_OPS(NULL, pcmcia_socket_dev_resume)
which based on CONFIG_PM_SLEEP may or may not actually
use its second parameter.

Signed-off-by: Maciej Żenczykowski <zenczykowski@gmail.com>
Signed-off-by: Dominik Brodowski <linux@dominikbrodowski.net>