atm: zatm: constify pci_device_id.

pci_device_id are not supposed to change at runtime. All functions
working with pci_device_id provided by <linux/pci.h> work with
const pci_device_id. So mark the non-const structs as const.

File size before:
   text	   data	    bss	    dec	    hex	filename
  14350	    352	     40	  14742	   3996	drivers/atm/zatm.o

File size After adding 'const':
   text	   data	    bss	    dec	    hex	filename
  14446	    256	     40	  14742	   3996	drivers/atm/zatm.o

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/atm/zatm.c

@@ -1642,7 +1642,7 @@ out_free:
 
 MODULE_LICENSE("GPL");
 
-static struct pci_device_id zatm_pci_tbl[] = {
+static const struct pci_device_id zatm_pci_tbl[] = {
 	{ PCI_VDEVICE(ZEITNET, PCI_DEVICE_ID_ZEITNET_1221), ZATM_COPPER },
 	{ PCI_VDEVICE(ZEITNET, PCI_DEVICE_ID_ZEITNET_1225), 0 },
 	{ 0, }