samples: fix path to tensorflow lite micro examples

The samples under the tensorflow modules directory has been renamed
since commit 6fd1b024. However, the path
in their README.rst was not updated.

Additionnaly, the modules top directory under the samples is missing for
the samples magic_wand and tflm_ethosu.

This fixes the path to the tensorflow lite micro samples in their
README.rst.

Signed-off-by: Gaël PORTAY <gael.portay@rtone.fr>