sfc: Search VPD with pci_vpd_find_ro_info_keyword()

Use pci_vpd_find_ro_info_keyword() to search for keywords in VPD to
simplify the code.

Replace netif_err() with pci_err() because the netdevice isn't registered
yet, which results in very ugly messages.

Use kmemdup_nul() instead of open-coding it.

Link: https://lore.kernel.org/r/bf5d4ba9-61a9-2bfe-19ec-75472732d74d@gmail.com


Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>