pkg/wakaama: Wakaama doesn't build

[maxvankessel]

The wakaama package doesn't build, makefile include is invalid. File: pkg/wakaama/Makefile.include
INCLUDES += -I$(RIOTPKG)/wakaama/wakaama

Should be:
INCLUDES += -I$(RIOTPKG)/wakaama

Unsure why this happens now and not before.

[rfuentess]

I think this was addressed by @moenoel in #8610