azure: Use --board flag with sandbox_spl

At present there is only one board which uses sandbox SPL. But with
sandbox_noinst being added, this is no longer true. Add a --board flag
so that we just build one board on azure, as is done in gitlab.
Signed-off-by: NSimon Glass <sjg@chromium.org>
Reviewed-by: NTom Rini <trini@konsulko.com>

.azure-pipelines.yml

@@ -148,7 +148,7 @@ jobs:
           export UBOOT_TRAVIS_BUILD_DIR=/tmp/sandbox_spl
           export PYTHONPATH=${UBOOT_TRAVIS_BUILD_DIR}/scripts/dtc/pylibfdt
           export PATH=${UBOOT_TRAVIS_BUILD_DIR}/scripts/dtc:${PATH}
-          ./tools/buildman/buildman -T0 -o ${UBOOT_TRAVIS_BUILD_DIR} -w sandbox_spl
+          ./tools/buildman/buildman -T0 -o ${UBOOT_TRAVIS_BUILD_DIR} -w --board sandbox_spl
           ./tools/binman/binman --toolpath ${UBOOT_TRAVIS_BUILD_DIR}/tools test
           ./tools/buildman/buildman -t
           ./tools/dtoc/dtoc -t