sparc32: mm: srmmu: add __ro_after_init to sparc32_cachetlb_ops structures

The objects viking_ops, viking_sun4d_smp_ops and smp_cachetlb_ops of
type sparc32_cachetlb_ops are not modified anywhere after getting modified
in the init functions. Inside init their reference is also stored in a
pointer of type const struct sparc32_cachetlb_ops *. So these structures
are never modified after init, therefore add __ro_after to the declaration
of these structures.

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: David S. Miller <davem@davemloft.net>