thermal: int340x_thermal: 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
   3152	   1096	      8	   4256	   10a0	processor_thermal_device.o

File size After adding 'const':
   text	   data	    bss	    dec	    hex	filename
   3216	   1032	      8	   4256	   10a0	processor_thermal_device.o
Signed-off-by: NArvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: NZhang Rui <rui.zhang@intel.com>

drivers/thermal/int340x_thermal/processor_thermal_device.c

@@ -127,7 +127,7 @@ static struct attribute *power_limit_attrs[] = {
 	NULL
 };
 
-static struct attribute_group power_limit_attribute_group = {
+static const struct attribute_group power_limit_attribute_group = {
 	.attrs = power_limit_attrs,
 	.name = "power_limits"
 };