Fix struct vs. class mismatches

Fix something being declared a struct and forward-declared a class and
vice versa.

gcc doesn't care, clang complains about the mismatch.

Change-Id: I7a7a8e9040e3c86fa1d73eb112631ea140861657
Signed-off-by: Bernhard Rosenkränzer <Bernhard.Rosenkranzer@linaro.org>