sh_eth: simplify sh_eth_check_reset()

The *while* loop in this function  can be turned into a normal *for* loop.
And getting rid  of the  single return point saves us a few more LoCs...

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: David S. Miller <davem@davemloft.net>