vhost: scsi: constify target_core_fabric_ops structures

Declare target_core_fabric_ops strucrues as const as they are only
passed as an argument to the functions target_register_template and
target_unregister_template. The arguments are of type const struct
target_core_fabric_ops *, so target_core_fabric_ops structures having
this property can be declared const.
Done using Coccinelle:

@r disable optional_qualifier@
identifier i;
position p;
@@
static struct target_core_fabric_ops i@p={...};

@ok@
position p;
identifier r.i;
@@
(
target_register_template(&i@p)
|
target_unregister_template(&i@p)
)
@bad@
position p!={r.p,ok.p};
identifier r.i;
@@
i@p

@depends on !bad disable optional_qualifier@
identifier r.i;
@@
+const
struct target_core_fabric_ops i;

File size before: drivers/vhost/scsi.o
   text	   data	    bss	    dec	    hex	filename
  18063	   2985	     40	  21088	   5260	drivers/vhost/scsi.o

File size after: drivers/vhost/scsi.o
   text	   data	    bss	    dec	    hex	filename
  18479	   2601	     40	  21120	   5280	drivers/vhost/scsi.o

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Acked-by: Jason Wang <jasowang@redhat.com>