usertools: read PCI device name as UTF-8

usertools: read PCI device name as UTF-8

Fixes the case where a PCI device string identifier
contains non-ASCII UTF-8

A particular example is Mellanox Connext-X 5 EN MT27800:

28:00.0 Ethernet controller: Mellanox Technologies
MT27800 Family [ConnectX-5]

Subsystem: Mellanox Technologies ConnectX®-5 EN network
interface card, 100GbE single-port QSFP28, PCIe3.0 x16,
tall bracket; MCX515A-CCAT

Signed-off-by: Christos Ricudis <ricudis@niometrics.com>
Acked-by: Andrew Rybchenko <arybchenko@solarflare.com>