test/dbus-device-reservation: fix include path

The extra `../` only works if the build directory is an immediate child of the
source directory. In all the other configurations this breaks the build.

Dropping the extra `../` makes use of the `-I${SOURCE_DIR}` provided by meson.

Signed-off-by: Eric Engestrom <eric@engestrom.ch>
1 job for fix-include in 2 minutes and 52 seconds
Status Job ID Name Coverage
  Test
passed #2613645
build

00:02:52