'struct k3_ring_ops' is not modified in this driver.

Constifying this structure moves some data to a read-only section, so
increase overall security.

On a x86_64, with allmodconfig:
Before:
======
   text	   data	    bss	    dec	    hex	filename
  17090	   3304	     32	  20426	   4fca	drivers/soc/ti/k3-ringacc.o

After:
=====
   text	   data	    bss	    dec	    hex	filename
  17266	   3144	     32	  20442	   4fda	drivers/soc/ti/k3-ringacc.o
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/cb9dfc18cdf890afa2c53cd74b0b330d6f1c30ab.1720546863.git.christophe.jaillet@wanadoo.frSigned-off-by: Nishanth Menon <nm@ti.com>