deps/Makefile: Add missing "git fetch" to /update and /clean targets

When the Makefile was modified to use a new tag/hash of a given
repo, the "make update" or "make clean" target will fail as the
new version/tag is not yet known to the local repo, only to the
remote (and hence we need a fetch).

Change-Id: I52c44c744674cd4dab0c85086d68bde6f9be1fca
1 file changed