During the process of building the BOM file the output of dh_dwarf2sources
is parsed to get the list of files used to build the binary. In order to
do that the script scans for json files on the doc folder, however since
some packages ship json files this leads to errors.

Fix this by only taking into account files generated by dh_dwarf2sources
which end in "_bin2sources.json".

Signed-off-by: Walter Lozano <walter.lozano@collabora.com>