west.yml: Update zephyr for sof/imx-stable-v2.15.5

We use NXP IMX Zephyr stable branch - imx-v4.3.5 branch
from nxp-upstream zephyr repo.

Signed-off-by: Daniel Baluta <Daniel Baluta daniel.baluta@gmail.com>

Author: Daniel Baluta

west.yml

@@ -10,7 +10,7 @@ manifest:
     - name: thesofproject
       url-base: https://github.com/thesofproject
     - name: zephyrproject
-      url-base: https://github.com/zephyrproject-rtos
+      url-base: https://github.com/nxp-upstream
 
   # When upgrading projects here please run git log --oneline in the
   # project and if not too long then include the output in your commit