sfc: Convert firmware subtypes to native byte order in efx_mcdi_get_b…
…oard_cfg()

On big-endian systems the MTD partition names currently have mangled
subtype numbers and are not recognised by the firmware update tool
(sfupdate).

Signed-off-by: Ben Hutchings <bhutchings@solarflare.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>