bnxt_en: Treat health register value 0 as valid in bnxt_try_reover_fw().

The retry loop in bnxt_try_recover_fw() should not abort when the
health register value is 0.  It is a valid value that indicates the
firmware is booting up.

Fixes: 861aae78

 ("bnxt_en: Enhance retry of the first message to the firmware.")
Reviewed-by: Edwin Peer <edwin.peer@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>