FST: fix symlink lookup handling in DevMap
symlink lookup can return a relative path, with was not handled correctly previously. It's verified on my test system:
$ eos fs status 2
[...]
stat.disk.load := 0.000067
stat.disk.readratemb := 0.000000
stat.disk.writeratemb := 0.002082
[...]
Previous commit 9fe5b580 was incomplete
Best, Erich