mmc: omap_hsmmc: 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
  11586	    624	      0	  12210	   2fb2	drivers/mmc/host/omap_hsmmc.o

File size After adding 'const':
   text	   data	    bss	    dec	    hex	filename
  11778	    432	      0	  12210	   2fb2	drivers/mmc/host/omap_hsmmc.o

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>