bnxt_en: Fix for system hang if request_irq fails

Fix bug in the error code path when bnxt_request_irq() returns failure.
bnxt_disable_napi() should not be called in this error path because
NAPI has not been enabled yet.

Fixes: c0c050c5 ("bnxt_en: New Broadcom ethernet driver.")
Signed-off-by: Vikas Gupta <vikas.gupta@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>