platform/x86: compal-laptop: constify attribute_group structures.

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

File size before:
   text	   data	    bss	    dec	    hex	filename
   6781	   6144	     34	  12959	   329f	drivers/platform/x86/compal-laptop.o

File size After adding 'const':
   text	   data	    bss	    dec	    hex	filename
   6845	   6080	     34	  12959	   329f	drivers/platform/x86/compal-laptop.o

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>