f2fs: constify super_operations

super_operations are not supposed to change at runtime.
"struct super_block" working with super_operations provided
by <linux/fs.h> work with const super_operations. So mark
the non-const structs as const
Signed-off-by: NArvind Yadav <arvind.yadav.cs@gmail.com>
Reviewed-by: NChao Yu <yuchao0@huawei.com>
Signed-off-by: NJaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/super.c

@@ -1546,7 +1546,7 @@ void f2fs_quota_off_umount(struct super_block *sb)
 }
 #endif
 
-static struct super_operations f2fs_sops = {
+static const struct super_operations f2fs_sops = {
 	.alloc_inode	= f2fs_alloc_inode,
 	.drop_inode	= f2fs_drop_inode,
 	.destroy_inode	= f2fs_destroy_inode,