xfs: simplify xfs_calc_dquots_per_chunk

ndquots is a 32-bit value, and we don't care
about the remainder; there is no reason to use do_div
here, it seems to be the result of a decade+ historical
accident.

Worse, the do_div implementation in userspace breaks
when fed a 32-bit dividend, so we commented it out there
in any case.

Change to simple division, and then we can change
userspace to match, and mandate a 64-bit dividend in
the do_div() in userspace as well.
Signed-off-by: Eric Sandeen <sandeen@redhat.com>

fs/xfs/libxfs/xfs_dquot_buf.c

@@ -35,13 +35,8 @@ int
 xfs_calc_dquots_per_chunk(
 	unsigned int		nbblks)	/* basic block units */
 {
-	unsigned int	ndquots;
-
 	ASSERT(nbblks > 0);
-	ndquots = BBTOB(nbblks);
-	do_div(ndquots, sizeof(xfs_dqblk_t));
-
-	return ndquots;
+	return BBTOB(nbblks) / sizeof(xfs_dqblk_t);
 }
 
 /*