firmware: rename struct firmware_priv to struct fw_sysfs

The struct firmware_priv is only used for the sysfs fallback
mechanism, rename it to make emphasis of this. This will also
enable us to use the name later for something much more
meaninful.

Signed-off-by: Luis R. Rodriguez <mcgrof@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>