net/bnxt: fix flow error on filter creation

net/bnxt: fix flow error on filter creation

If set_em_filter/set_ntuple_filter cmds fails for some reason,
driver is not filling the "rte_flow_error" string buffer.
Same is the case when flow create fails due to an already
existing mark id for the new flow id created.
This leads to a crash in testpmd while trying to print the
error message.

Fixes: 5c1171c97216 ("net/bnxt: refactor filter/flow")
Fixes: 9db66782bd06 ("net/bnxt: fix supporting zero mark ID with RSS action")
Cc: stable@dpdk.org
Signed-off-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Reviewed-by: Ajit Khaparde <ajit.khaparde@broadcom.com>