travis: Always use the branch from the committer

Regardless if it is a push or a pull request, Travis will use the
committers repository and branch. For developers this means his own
branch will be used when pushing to his own gits and when making a pull
request. When the pull request is merged, which is seen as normal push
to the upstream repository, Travis will once more build according to the
definition, but this time use the upstream repository and the tip branch
instead.

Signed-off-by: Joakim Bech <joakim.bech@linaro.org>
Reviewed-by: Igor Opaniuk <igor.opaniuk@linaro.org>

.travis.yml

@@ -57,6 +57,14 @@ script:
   - if [ $REPO_PROJ == "qemu_v8" ]; then cd $HOME/$REPO_PROJ/qemu && git submodule update --init dtc; fi
   # Here we are using Travis environment variables to select the correct branch
   # based on either a pull request or a normal push.
-  - cd $HOME/$REPO_PROJ/build && git remote add github https://github.com/$TRAVIS_REPO_SLUG && git remote update
-  - cd $HOME/$REPO_PROJ/build && git checkout github/$TRAVIS_BRANCH
+  - |
+        if [ "$TRAVIS_EVENT_TYPE" == "pull_request" ]; then
+                slug=$TRAVIS_PULL_REQUEST_SLUG
+                branch=$TRAVIS_PULL_REQUEST_BRANCH
+        else
+                slug=$TRAVIS_REPO_SLUG
+                branch=$TRAVIS_BRANCH
+        fi
+  - cd $HOME/$REPO_PROJ/build && git remote add github https://github.com/$slug && git remote update
+  - cd $HOME/$REPO_PROJ/build && git checkout github/$branch
   - cd $HOME/$REPO_PROJ/build && make -f toolchain.mk toolchains -j3 && make all -j`nproc`