xfs: kill meaningless variable 'zero'

In xfs_file_aio_write_checks(), variable 'zero' is there only to
satisfy xfs_zero_eof(), the result of it is ignored. Now, with
iomap_zero_range() based xfs_zero_eof(), we can safely pass NULL as
the last param of it and kill 'zero'.

Signed-off-by: Eryu Guan <eguan@redhat.com>
Reviewed-by: Carlos Maiolino <cmaiolino@redhat.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_file.c

@@ -377,8 +377,6 @@ restart:
 	 */
 	spin_lock(&ip->i_flags_lock);
 	if (iocb->ki_pos > i_size_read(inode)) {
-		bool	zero = false;
-
 		spin_unlock(&ip->i_flags_lock);
 		if (!drained_dio) {
 			if (*iolock == XFS_IOLOCK_SHARED) {
@@ -399,7 +397,7 @@ restart:
 			drained_dio = true;
 			goto restart;
 		}
-		error = xfs_zero_eof(ip, iocb->ki_pos, i_size_read(inode), &zero);
+		error = xfs_zero_eof(ip, iocb->ki_pos, i_size_read(inode), NULL);
 		if (error)
 			return error;
 	} else