zephyr: tests: Disable ack_required in proxy_usb_mux
zephyr: tests: Disable ack_required in proxy_usb_mux

Set ack_required to false in proxy_hpd_update and proxy_set functions.
In test environment there is not possible to get ACK from AP which is
not emulated, so returning ack_required == true, actually only introduce
delay. During this delay, other thread may perform operation on USB mux
which disturb test. To prevent that, ack_required is forced to false by
proxy_usb_mux.

BUG=b:238860999
TEST=zmake test test-drivers
BRANCH=None

Signed-off-by: Tomasz Michalec <a547db31280d14f095c760a23a7523d0b1e55fe6@semihalf.com>
Change-Id: I6817e99461498beeacf639e3f457c64e5ddde874
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3758220
Commit-Queue: Tomasz Michalec <c064a6042954d4ba0805003dc021b76413ff1548@google.com>
Reviewed-by: Wai-Hong Tam <04b587fdf5845741a0c5a8b9cd59ca72d73ef8fc@google.com>
Tested-by: Tomasz Michalec <c064a6042954d4ba0805003dc021b76413ff1548@google.com>

coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec,coreboot/chrome-ec