bnxt_en: Return from timer if interface is not in open state.

This will avoid many uneccessary error logs when driver or firmware is
in reset.

Fixes: 230d1f0d ("bnxt_en: Handle firmware reset.")
Signed-off-by: Vasundhara Volam <vasundhara-v.volam@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>