scsi: target: Constify struct configfs_item_operations and configfs_group_operations

scsi: target: Constify struct configfs_item_operations and configfs_group_operations

'struct configfs_item_operations' and 'configfs_group_operations' are
not modified in this driver.

Constifying these structures moves some data to a read-only section, so
increases overall security, especially when the structure holds some
function pointers.

On a x86_64, with allmodconfig:
Before:
======
   text	   data	    bss	    dec	    hex	filename
 151831	  80058	   4832	 236721	  39cb1	drivers/target/target_core_configfs.o
  45200	  16658	      0	  61858	   f1a2	drivers/target/target_core_fabric_configfs.o

After:
=====
   text	   data	    bss	    dec	    hex	filename
 152599	  79290	   4832	 236721	  39cb1	drivers/target/target_core_configfs.o
  46352	  15506	      0	  61858	   f1a2	drivers/target/target_core_fabric_configfs.o

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://patch.msgid.link/a0f25237ae86b8c4dd7a3876c4ed2dc3de200173.1767008082.git.christophe.jaillet@wanadoo.fr
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>