video: fbdev: riva: 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
  13285	   2080	      3	  15368	   3c08	video/fbdev/riva/fbdev.o

File size after adding 'const':
   text	   data	    bss	    dec	    hex	filename
  14677	    688	      3	  15368	   3c08	video/fbdev/riva/fbdev.o

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Cc: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Antonino Daplas <adaplas@gmail.com>
Cc: Maik Broemme <mbroemme@libmpq.org>
Cc: Florian Tobias Schandinat <FlorianSchandinat@gmx.de>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>

drivers/video/fbdev/riva/fbdev.c

@@ -101,7 +101,7 @@ static int rivafb_blank(int blank, struct fb_info *info);
  *
  * ------------------------------------------------------------------------- */
 
-static struct pci_device_id rivafb_pci_tbl[] = {
+static const struct pci_device_id rivafb_pci_tbl[] = {
 	{ PCI_VENDOR_ID_NVIDIA_SGS, PCI_DEVICE_ID_NVIDIA_SGS_RIVA128,
 	  PCI_ANY_ID, PCI_ANY_ID, 0, 0, 0 },
 	{ PCI_VENDOR_ID_NVIDIA, PCI_DEVICE_ID_NVIDIA_TNT,