static-checks: use `remotes/origin/master` instead of `master`

This is a safer approach in cases where master local branch does not
exist, i.e. shadow cloning.

Signed-off-by: Leonardo Sandoval <leonardo.sandoval@linaro.org>
Change-Id: I2fdae51673169d4c32d3f308c2eb3fd885c42e76
2 files changed