platform/x86: toshiba_haps: constify haps_attr_group

File size before:
   text	   data	    bss	    dec	    hex	filename
   1471	    528	      8	   2007	    7d7	drivers/platform/x86/toshiba_haps.o

File size After adding 'const':
   text	   data	    bss	    dec	    hex	filename
   1519	    464	      8	   1991	    7c7	drivers/platform/x86/toshiba_haps.o

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>