bnx2: avoid compiler warnings

drivers/net/bnx2.c: In function ‘bnx2_enable_forced_2g5’:
drivers/net/bnx2.c:1447: warning: ‘bmcr’ may be used uninitialized in this function
drivers/net/bnx2.c: In function ‘bnx2_disable_forced_2g5’:
drivers/net/bnx2.c:1482: warning: ‘bmcr’ may be used uninitialized in this function

One fix would be to have an initial value, but a plain return might be better.

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>