Fix race condition in nanopb_generator.py

Fix FileExistsError build failure caused by a race condition in the
output directory creation of nanopb_generator.py.

Signed-off-by: Imre Kis <imre.kis@arm.com>
Change-Id: Ie956e3b27190df5cb9f692f0818d0344d6fd7cc0
2 files changed