firmware loader: log path to loaded firmwares

This is useful for users who are trying to identify the firmwares in use
on their system.

Signed-off-by: Drew DeVault <sir@cmpwn.com>
Link: https://lore.kernel.org/r/20191103180646.34880-1-sir@cmpwn.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>