xfs: remove unused parameter from xfs_writepage_map

The first thing that xfs_writepage_map does is clobber the offset
parameter.  Since we never use the passed-in value, turn the parameter
into a local variable.  This gets rid of an UBSAN warning in generic/466.
Signed-off-by: NDarrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: NBrian Foster <bfoster@redhat.com>

fs/xfs/xfs_aops.c

@@ -896,13 +896,13 @@ xfs_writepage_map(
 	struct writeback_control *wbc,
 	struct inode		*inode,
 	struct page		*page,
-	loff_t			offset,
-	uint64_t              end_offset)
+	uint64_t		end_offset)
 {
 	LIST_HEAD(submit_list);
 	struct xfs_ioend	*ioend, *next;
 	struct buffer_head	*bh, *head;
 	ssize_t			len = i_blocksize(inode);
+	uint64_t		offset;
 	int			error = 0;
 	int			count = 0;
 	int			uptodate = 1;
@@ -1146,7 +1146,7 @@ xfs_do_writepage(
 		end_offset = offset;
 	}
 
-	return xfs_writepage_map(wpc, wbc, inode, page, offset, end_offset);
+	return xfs_writepage_map(wpc, wbc, inode, page, end_offset);
 
 redirty:
 	redirty_page_for_writepage(wbc, page);