devargs: fix crash on failure

devargs: fix crash on failure

This problem was discovered when passing invalid PCI id to the
blacklist API in devargs.

Any failures in rte_devargs_add would cause a core dump because
it would call rte_log() before the the EAL log environment was
initialized.  Rather than try and log just remove the messages
and leave it up to the caller to check the return value.

Most of the other failure possibilities are when malloc() fails, and if
that happens any logging that used malloc() would also fail.

This failure was not caught by the standalone tests to devargs
because the tests are run after calling rte_eal_init (which is not
how devargs is intended to be used).

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Acked-by: Olivier Matz <olivier.matz@6wind.com>