mfd: kempld-core: Constify variables that point to const structure

Add const to the declaration of various local variables of type
kempld_platform_data for which the referenced value is always only
dereferenced or passed to a const parameter, to record the fact that
kempld_platform_data_generic is declared as const.

The semantic match that finds this issue is as follows:
(http://coccinelle.lip6.fr/

)

// <smpl>
@r@
identifier i,j;
@@
const struct i j = { ... };

@ok@
identifier r.i;
position p;
@@
const struct i@p *

@@
identifier r.i;
position p != ok.p;
@@
* struct i@p *
// </smpl>

Signed-off-by: Julia Lawall <Julia.Lawall@lip6.fr>
Signed-off-by: Lee Jones <lee.jones@linaro.org>