pcmcia: hide the MAC address helpers if !NET

pcmcia_get_mac_from_cis is only called from networking and
recent changes made it call dev_addr_mod() which is itself
only defined if NET.

Reported-by: kernel test robot <lkp@intel.com>
Fixes: adeef3e3 ("net: constify netdev->dev_addr")
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>