ASoC: rsnd: constify dev_pm_ops structures.

dev_pm_ops are not supposed to change at runtime. All functions
working with dev_pm_ops provided by <linux/device.h> work with const
dev_pm_ops. So mark the non-const structs as const.

File size before:
   text	   data	    bss	    dec	    hex	filename
   8172	    920	      0	   9092	   2384	sound/soc/sh/rcar/core.o

File size After adding 'const':
   text	   data	    bss	    dec	    hex	filename
   8364	    728	      0	   9092	   2384	sound/soc/sh/rcar/core.o

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>