fs: xfs: libxfs: constify xfs_nameops structures

Declare the structure xfs_nameops as const as it is only stored in the
m_dirnameops field of a xfs_mount structure. This field is of type
const struct xfs_nameops *, so xfs_nameops structures having this
property can be declared as const.
Done using Coccinelle:
@r1 disable optional_qualifier @
identifier i;
position p;
@@
static struct xfs_nameops i@p = {...};

@ok1@
identifier r1.i;
position p;
struct xfs_mount mp;
@@
mp.m_dirnameops=&i@p

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

@depends on !bad disable optional_qualifier@
identifier r1.i;
@@
static
+const
struct xfs_nameops i={...};

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

File size before:
   text	   data	    bss	    dec	    hex	filename
   5302	     85	      0	   5387	   150b	fs/xfs/libxfs/xfs_dir2.o

File size after:
   text	   data	    bss	    dec	    hex	filename
   5318	     69	      0	   5387	   150b	fs/xfs/libxfs/xfs_dir2.o

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>