phy: cadence-torrent: Constify struct cdns_reg_pairs

'struct cdns_reg_pairs' 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
  78154	  20222	     16	  98392	  18058	drivers/phy/cadence/phy-cadence-torrent.o

After:
=====
   text	   data	    bss	    dec	    hex	filename
  85130	  13214	     16	  98360	  18038	drivers/phy/cadence/phy-cadence-torrent.o
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/803684a6f0c24d7e091dc8d285dd49c6fd31a010.1720718240.git.christophe.jaillet@wanadoo.frSigned-off-by: Vinod Koul <vkoul@kernel.org>