The mpxy_rpmi_mbox_data is provided by RPMI service group specific
MPXY driver to the common MPXY RPMI mailbox client implementation
so let's constantify mpxy_rpmi_mbox_data in mpxy_rpmi_mbox so that
it is not accidently modified.
Signed-off-by: Anup Patel <apatel@ventanamicro.com>
Reviewed-by: Samuel Holland <samuel.holland@sifive.com>