zephyr: test: fix build warning about missing register
zephyr: test: fix build warning about missing register

This is a quick fix to allow the build to finish without warning. The
reality is that this should be collapsed into a single node. Effectively,
cros,ps8xxx-emul is a child class/emulator of cros,tcpci-emul.

BRANCH=none
BUG=none
TEST=zmake configure --test test-drivers

Signed-off-by: Yuval Peress <50dc11c009bd4d7e9d9d15a383c1743ce5ee82ef@google.com>
Change-Id: Id665474deec59906b967c9f0c26e7d32b2bb5869
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/ec/+/3500294
Reviewed-by: Al Semjonovs <c3a2ecb550cad1e7d5a943ca6241377f7b43ffc4@google.com>

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