regulator: 88pm800: constify regulator_ops structures

Declare regulator_ops structures as const as they are 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/88pm800.o
   text	   data	    bss	    dec	    hex	filename
   1001	   6288	      0	   7289	   1c79	drivers/regulator/88pm800.o

File size after: drivers/regulator/88pm800.o
   text	   data	    bss	    dec	    hex	filename
   1513	   5776	      0	   7289	   1c79	drivers/regulator/88pm800.o

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