scripts: sd_fusing: support device symlinks in ensure_parttable()

scripts: sd_fusing: support device symlinks in ensure_parttable()

sd_fusing needs to support referring to devices by symlinks created by udev like
/dev/disk/by-id/usb-Generic_STORAGE_DEVICE_000000000272-0. Their partitions
are named /dev/disk/by-id/usb-Generic_STORAGE_DEVICE_000000000272-0-partX. Therefore
there is no universal way to access both /dev/sdXY and the symlinked
partitions and using get_partition_device() is the way to go.

Change-Id: I4c586f8e9b6e3940faa6055c90835bbff1777ec5
Fixes: 43ab41c7e7 ("sd_fusing.py: Ensure selected flashing target actually matches what is on device")
Signed-off-by: Łukasz Stelmach <l.stelmach@samsung.com>