hw/nvram/mac_nvram: Report failure to write data

hw/nvram/mac_nvram: Report failure to write data

There's no way for the macio_nvram device to report failure to write
data, but we can at least report it to the user with error_report()
as we do in other devices like xlnx-efuse.

Spotted by Coverity.

Resolves: Coverity CID 1507628
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20240312183810.557768-6-peter.maydell@linaro.org