bnxt_en: Fix invoking hwmon_notify_event

FW sends the async event to the driver when the device temperature goes
above or below the threshold values.  Only notify hwmon if the
temperature is increasing to the next alert level, not when it is
decreasing.

Cc: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Kashyap Desai <kashyap.desai@broadcom.com>
Reviewed-by: Somnath Kotur <somnath.kotur@broadcom.com>
Signed-off-by: Kalesh AP <kalesh-anakkur.purayil@broadcom.com>
Signed-off-by: Michael Chan <michael.chan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>