usertools: fix refresh binding infos

usertools: fix refresh binding infos

Currently clear_data (dpdk-devbind.py) doesn't work as expected
since "global devices" is missing and so "devices" is considered
a local variable.

This commit changes "clear_data" function in order to really clear
devices by adding "global devices".

Fixes: ea9f00f7289a ("usertools: refactor NIC and crypto binding details")
Cc: stable@dpdk.org
Signed-off-by: Timothy Redaelli <tredaelli@redhat.com>
Acked-by: Luca Boccassi <bluca@debian.org>
Reviewed-by: David Marchand <david.marchand@redhat.com>