bnxt_en: Fix reporting of test result in ethtool selftest

When the selftest command fails, driver is not reporting the failure
by updating the "test->flags" when bnxt_close_nic() fails.

Fixes: eb513658

 ("bnxt_en: Add basic ethtool -t selftest support.")
Reviewed-by: Pavan Chebbi <pavan.chebbi@broadcom.com>
Reviewed-by: Somnath Kotur <somnath.kotur@broadcom.com>
Signed-off-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>