ci: Fix xtensa-sample_controller_zephyr-elf test platform identifier

`qemu_xtensa` was renamed to `qemu_xtensa/dc233c`.

Signed-off-by: Stephanos Ioannidis <[email protected]>

.github/workflows/ci.yml

@@ -1738,7 +1738,7 @@ jobs:
                 # upstream user platform is currently available.
                 ;;
               xtensa-sample_controller_zephyr-elf)
-                PLATFORM_ARGS+="-p qemu_xtensa "
+                PLATFORM_ARGS+="-p qemu_xtensa/dc233c "
                 ;;
               xtensa-sample_controller32_zephyr-elf)
                 # xtensa-sample_controller32_zephyr-elf is untested because no