greybus: Revert "update UniPro Set Interface Power Mode operation to match spec"

This reverts commit 29fee8c55b59bb6ac59b99a0563c89c514cba42b.

This change and its companion NuttX changes seem to be triggering a
storm of POWERMODEIND switch interrupts on the SVC.

Signed-off-by: Jeffrey Carlyle <jcarlyle@google.com>
Acked-by: Sandeep Patil <sspatil@google.com>