libata and bogus LBA48 drives

A colleague noticed recent versions of Ubuntu no longer detect his 80 GB
ST380020ACE drive. This drive is special in that it advertises LBA48 support,
but has the lba_capacity_2 field set to zero (cfr.
http://lkml.org/lkml/2004/3/30/163).

Upon closer look, libata indeed doesn't seem to handle this case yet.
Below is an (untested) fix.
Signed-off-by: Jeff Garzik <jeff@garzik.org>

include/linux/ata.h

@@ -425,6 +425,8 @@ static inline int ata_id_has_lba48(const u16 *id)
 {
 	if ((id[83] & 0xC000) != 0x4000)
 		return 0;
+	if (!ata_id_u64(id, 100))
+		return 0;
 	return id[83] & (1 << 10);
 }