tests: Fix partmap_test for arm*-efi, disk numbering has changed

Perhaps using a newer UEFI firmware is the reason for the created test disk
showing up as hd2 instead of hd3.

Signed-off-by: Glenn Washburn <development@efficientek.com>
Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>

tests/partmap_test.in

@@ -89,7 +89,7 @@ case "${grub_modinfo_target_cpu}-${grub_modinfo_platform}" in
 	disk=arc/scsi0/disk0/rdisk0
 	;;
     arm*-efi)
-	disk=hd3
+	disk=hd2
 	;;
     *)
 	disk=hd0