pcmcia: ds: convert to use DRIVER_ATTR_RO

We are trying to get rid of DRIVER_ATTR(), and the pcmcia driver's
attribute can be trivially changed to use DRIVER_ATTR_RO().

Cc: Russell King <rmk+kernel@armlinux.org.uk>
Cc: <linux-pcmcia@lists.infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>