pinctrl: ti: ti-iodelay: Constify struct ti_iodelay_reg_data

pinctrl: ti: ti-iodelay: Constify struct ti_iodelay_reg_data

'struct ti_iodelay_reg_data' 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
  17259	   1788	     16	  19063	   4a77	drivers/pinctrl/ti/pinctrl-ti-iodelay.o

After:
=====
   text	   data	    bss	    dec	    hex	filename
  17355	   1692	     16	  19063	   4a77	drivers/pinctrl/ti/pinctrl-ti-iodelay.o

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/40d6e67ab4e73d2cbe7ca0060ac27afc894fc415.1720556038.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>