disk: initialize name/part fields when returning a whole disk

When get_device_and_partition() finds a disk without a partition table,
under some conditions, it "returns" a disk_partition_t that describes
the entire raw disk. Make sure to initialize all fields in the partition
descriptor in that case.

The value chosen for name is just some arbitrary descriptive string.

The value chosen for info matches the check at the end of
get_device_and_partition(). However, it's probably not that important;
it's not obvious that the value is really used.

Reported-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Signed-off-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Benoît Thébaudeau <benoit.thebaudeau@advansee.com>
Signed-off-by: Tom Rini <trini@ti.com>