samples: code_relocation: Disable code coverage.

Currently coverage is enabled only in platforms which dont have
multiple memory regions. This sample was designed to emulate
different memory regions. This in conjunction with gcov which
might instrument data in different memory regions will not work
as expected. Therefore disabling gcov for this sample.

Fixes: GH-15107

Signed-off-by: Adithya Baglody <adithya.nagaraj.baglody@intel.com>