net: xilinx: constify net_device_ops structure

Declare net_device_ops structure as const as it is only stored in
the netdev_ops field of a net_device structure. This field is of type
const, so net_device_ops structures having same properties can be made
const too.
Done using Coccinelle:

@r1 disable optional_qualifier@
identifier i;
position p;
@@
static struct net_device_ops i@p={...};

@ok1@
identifier r1.i;
position p;
struct net_device ndev;
@@
ndev.netdev_ops=&i@p

@bad@
position p!={r1.p,ok1.p};
identifier r1.i;
@@
i@p

@depends on !bad disable optional_qualifier@
identifier r1.i;
@@
+const
struct net_device_ops i;

File size before:
   text	   data	    bss	    dec	    hex	filename
   6201	    744	      0	   6945	   1b21 ethernet/xilinx/xilinx_emaclite.o

File size after:
   text	   data	    bss	    dec	    hex	filename
   6745	    192	      0	   6937	   1b19 ethernet/xilinx/xilinx_emaclite.o

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>