xfs: remove redundant re-initialization of total_nr_pages

Variable total_nr_pages is being initialized and then updated with
the same value, this latter assignment is redundant and can be
removed.  Cleans up clang build warning:

Value stored to 'total_nr_pages' during its initialization is never read
Signed-off-by: Colin Ian King <colin.king@canonical.com>
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_buf.c

@@ -1258,8 +1258,6 @@ xfs_buf_ioapply_map(
 	int		size;
 	int		offset;
 
-	total_nr_pages = bp->b_page_count;
-
 	/* skip the pages in the buffer before the start offset */
 	page_index = 0;
 	offset = *buf_offset;