This lets us cope with block device drivers that don't implement
HDIO_GETGEO. Fixes Ubuntu bug #1237519.
* grub-core/osdep/linux/hostdisk.c (sysfs_partition_path): New
function.
(sysfs_partition_start): Likewise.
(grub_util_find_partition_start_os): Try sysfs_partition_start
before HDIO_GETGEO.