Due to change in firmware flow, update mailbox writes to poll on ready bit
instead of run_busy bit. This change makes the polling method consistent
for both writes and reads, which also uses the ready bit.

Fixes: 2546c600 ("platform/x86: Add Intel Software Defined Silicon driver")
Signed-off-by: David E. Box <david.e.box@linux.intel.com>
Link: https://lore.kernel.org/r/20220420155622.1763633-3-david.e.box@linux.intel.comReviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>