doc: reduce whitespace in meson build file
doc: reduce whitespace in meson build file

For building the guides, we can make the meson.build easier to read by
using the subdir_done function to quit early.

Cc: stable@dpdk.org

Signed-off-by: Bruce Richardson <66b9e8e8fbd5e9f41f91b0af050876182ce9d0e4@intel.com>
Acked-by: Aaron Conole <aa17ba42a0685b214660ffb377dc7569a94d48c9@redhat.com>
Acked-by: Luca Boccassi <020748dc039465edc3ee6f30c530b21164cdce27@debian.org>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk