bnxt_en: Remove locking around txr->dev_state

txr->dev_state was not consistently manipulated with the acquisition of
the per-queue lock, after further inspection the lock does not seem
necessary, either the value is read as BNXT_DEV_STATE_CLOSING or 0.

Reported-by: coverity (CID 1339583)
Fixes: c0c050c5

 ("bnxt_en: New Broadcom ethernet driver.")
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Acked-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>