Earlier compilers such as GCC 4 do not like anynomous unions, make it a named
union "u", and update the code where relevant.
Fixes FS#298
Fixes: a72e1692b8 ("firmware-utils: Add support for the Cisco Meraki MX60/MX60W")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>