f2fs: support iopoll method

Wire up the iopoll method to the common implementation.
As f2fs use common dio infrastructure:
commit a1e09b03 ("f2fs: use iomap for direct I/O")
Signed-off-by: Wu Bo <bo.wu@vivo.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/file.c

@@ -4908,6 +4908,7 @@ const struct file_operations f2fs_file_operations = {
 	.llseek		= f2fs_llseek,
 	.read_iter	= f2fs_file_read_iter,
 	.write_iter	= f2fs_file_write_iter,
+	.iopoll		= iocb_bio_iopoll,
 	.open		= f2fs_file_open,
 	.release	= f2fs_release_file,
 	.mmap		= f2fs_file_mmap,