liblp: fix host lpdump cannot work issue

If a relative path is provided on linux host, lpdump will not
work because GetPartitionAbsolutePath return an incorrect pathname.

Test: lpdump super.img

Change-Id: I7d0f10110eb72745edba810bdf288e2506bfedd6
Signed-off-by: lijiazi <lijiazi@xiaomi.com>