teeacl: fix include path

The `uuid` pkg-config file provides the include directory as
`${PREFIX}/include/uuid`. Set include path relative to pkg-config file
specified include_dir to remain portable.

Signed-off-by: Eero Aaltonen <eero.aaltonen@vaisala.com>
Acked-by: Clement Faure <clement.faure@nxp.com>
Acked-by: Jens Wiklander <jens.wiklander@linaro.org>