bnx2x: Rework power state handling code

Move "don't shut down the power" logic into bnx2x_set_power_state() to make the code cleaner.

Signed-off-by: Vladislav Zolotarov <vladz@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>