platform/x86: sony-laptop: constify attribute_group and input index array

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.

The content of sony_laptop_input_index does not change and is declared
as a static global array.

Constify spic_attribute_group and sony_laptop_input_index.

File size before:
   text	   data	    bss	    dec	    hex	filename
  31273	   5176	    372	  36821	   8fd5	drivers/platform/x86/sony-laptop.o

File size After adding 'const':
   text	   data	    bss	    dec	    hex	filename
  31337	   5112	    372	  36821	   8fd5	drivers/platform/x86/sony-laptop.o

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
[dvhart: updated commit message, includes fix suggested by Arnd Bergmann]
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Darren Hart (VMware) <dvhart@infradead.org>