xfs: don't clear imap_valid for a non-uptodate buffers

Finding a buffer that isn't uptodate doesn't invalidate the mapping for
any given block.  The last_sector check will already take care of starting
another ioend as soon as we find any non-update buffer, and if the current
mapping doesn't include the next uptodate buffer the xfs_imap_valid check
will take care of it.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>

fs/xfs/xfs_aops.c

@@ -863,10 +863,8 @@ xfs_writepage_map(
 		 * meaningless for holes (!mapped && uptodate), so skip
 		 * buffers covering holes here.
 		 */
-		if (!buffer_mapped(bh) && buffer_uptodate(bh)) {
-			wpc->imap_valid = false;
+		if (!buffer_mapped(bh) && buffer_uptodate(bh))
 			continue;
-		}
 
 		if (buffer_unwritten(bh))
 			new_type = XFS_IO_UNWRITTEN;
@@ -879,11 +877,8 @@ xfs_writepage_map(
 				ASSERT(buffer_mapped(bh));
 			/*
 			 * This buffer is not uptodate and will not be
-			 * written to disk.  Ensure that we will put any
-			 * subsequent writeable buffers into a new
-			 * ioend.
+			 * written to disk.
 			 */
-			wpc->imap_valid = false;
 			continue;
 		}