tools: setup: fix #618, a path dependency issue

Signed-off-by: gsh1209 <gsh1209@outlook.com>

Author: gsh1209

tools/envsetup.sh

@@ -32,7 +32,7 @@ elif [ "${0##*/}" = "dash" ]; then
 fi
 # bootstrap OE
 echo "Init OE"
-export BASH_SOURCE="openembedded-core/oe-init-build-env"
+export BASH_SOURCE="${LAYERS_ROOT}/openembedded-core/oe-init-build-env"
 . ${LAYERS_ROOT}/openembedded-core/oe-init-build-env ${BUILD_DIR}
 
 # Symlink the cache