ata: pata_octeon_cf: make of_device_ids const.

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

File size before:
   text	   data	    bss	    dec	    hex	filename
    465	    696	      4	   1165	    48d	drivers/ata/pata_octeon_cf.o

File size after constify octeon_cf_match.
   text	   data	    bss	    dec	    hex	filename
    865	    280	      4	   1149	    47d	drivers/ata/pata_octeon_cf.o

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Tejun Heo <tj@kernel.org>