fs: add file_operations->uring_cmd_iopoll

io_uring will invoke this to do completion polling on uring-cmd
operations.

Signed-off-by: Kanchan Joshi <joshi.k@samsung.com>
Link: https://lore.kernel.org/r/20220823161443.49436-2-joshi.k@samsung.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/fs.h

@@ -2132,6 +2132,7 @@ struct file_operations {
 				   loff_t len, unsigned int remap_flags);
 	int (*fadvise)(struct file *, loff_t, loff_t, int);
 	int (*uring_cmd)(struct io_uring_cmd *ioucmd, unsigned int issue_flags);
+	int (*uring_cmd_iopoll)(struct io_uring_cmd *ioucmd);
 } __randomize_layout;
 
 struct inode_operations {