Declare regulator_ops structure as const as it is only stored in the ops
field of a regulator_desc structure. This field is of type const, so
regulator_ops structures having this property can be made const too.

File size before: drivers/regulator/pfuze100-regulator.o
   text	   data	    bss	    dec	    hex	filename
   3552	  12528	     16	  16096	   3ee0 regulator/pfuze100-regulator.o

File size after: drivers/regulator/pfuze100-regulator.o
   text	   data	    bss	    dec	    hex	filename
   4576	  11496	     16	  16088	   3ed8 regulator/pfuze100-regulator.o

Signed-off-by: Bhumika Goyal <bhumirks@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>