s390/zcrypt_queue: constify attribute_group structures.

attribute_group are not supposed to change at runtime. All functions
working with attribute_group 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
   1361	     96	      0	   1457	    5b1	s390/crypto/zcrypt_queue.o

File size After adding 'const':
   text	   data	    bss	    dec	    hex	filename
   1425	     32	      0	   1457	    5b1	s390/crypto/zcrypt_queue.o

Signed-off-by: Arvind Yadav <arvind.yadav.cs@gmail.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

drivers/s390/crypto/zcrypt_queue.c

@@ -89,7 +89,7 @@ static struct attribute *zcrypt_queue_attrs[] = {
 	NULL,
 };
 
-static struct attribute_group zcrypt_queue_attr_group = {
+static const struct attribute_group zcrypt_queue_attr_group = {
 	.attrs = zcrypt_queue_attrs,
 };