zephyr-env.sh: prepend to PATH

Currently, if you source this in one Zephyr tree and then
source it again in a second copy, the PATH will still
prefer tools and scripts the first Zephyr tree.

Change-Id: I658231025b155d19a2bffa25b8062be7ccd06da4
Signed-off-by: Andrew Boie <andrew.p.boie@intel.com>

zephyr-env.sh

@@ -52,7 +52,7 @@ export ZEPHYR_BASE=$( builtin cd "$( dirname "$DIR" )" && pwd ${MINGW_OPT})
 
 scripts_path=${ZEPHYR_BASE}/scripts
 echo "${PATH}" | grep -q "${scripts_path}"
-[ $? != 0 ] && export PATH=${PATH}:${scripts_path}
+[ $? != 0 ] && export PATH=${scripts_path}:${PATH}
 unset scripts_path
 
 # enable custom environment settings