travis-ci: use correct exit code on errors

The phrase "if [ $? -ne 0 ]; then exit $?; fi" doesn't work correctly;
by the time the "exit" statement runs, $? has already been over-written
by the result of the [ command. Fix this by explicitly storing $? and
then using that stored value in both the test and the error-case exit
statement.

This change also converts from textual comparison to integer comparison,
since the exit code is an integer and there's no need to convert it to
a string for comparison.

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Reviewed-by: Heiko Schocher <hs@denx.de>

.travis.yml

@@ -70,11 +70,12 @@ script:
  - if [[ "${BUILDMAN}" != "" ]]; then
      set +e;
      tools/buildman/buildman ${BUILDMAN};
-     if [[ "$?" == "0" || "$?" == "129" ]]; then
+     ret=$?;
+     if [[ $ret -eq 0 || $ret -eq 129 ]]; then
        exit 0;
      else
-       exit $?;
-     fi
+       exit $ret;
+     fi;
    fi
 
 matrix: