xfs: fix off-by-one error in xfs_rtalloc_query_range

In commit 8ad560d256 ("xfs: strengthen rtalloc query range checks")
we strengthened the input parameter checks in the rtbitmap range query
function, but introduced an off-by-one error in the process.  The call
to xfs_rtfind_forw deals with the high key being rextents, but we clamp
the high key to rextents - 1.  This causes the returned results to stop
one block short of the end of the rtdev, which is incorrect.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Allison Henderson <allison.henderson@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>

fs/xfs/libxfs/xfs_rtbitmap.c

@@ -1029,8 +1029,8 @@ xfs_rtalloc_query_range(
 	if (low_rec->ar_startext >= mp->m_sb.sb_rextents ||
 	    low_rec->ar_startext == high_rec->ar_startext)
 		return 0;
-	if (high_rec->ar_startext >= mp->m_sb.sb_rextents)
-		high_rec->ar_startext = mp->m_sb.sb_rextents - 1;
+	if (high_rec->ar_startext > mp->m_sb.sb_rextents)
+		high_rec->ar_startext = mp->m_sb.sb_rextents;
 
 	/* Iterate the bitmap, looking for discrepancies. */
 	rtstart = low_rec->ar_startext;