infiniband: mthca: constify pci_device_id.

infiniband: mthca: 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
  13067	    805	      4	  13876	   3634	infiniband/hw/mthca/mthca_main.o

File size After adding 'const':
   text	   data	    bss	    dec	    hex	filename
  13419	    453	      4	  13876	   3634	infiniband/hw/mthca/mthca_main.o

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>