sh_eth: Remove obsolete explicit clock handling for WoL

Currently, if Wake-on-LAN is enabled, the SH-ETH device's module clock
is manually kept running during system suspend, to make sure the device
stays active.

Since commits 91c719f5 ("soc: renesas: rcar-sysc: Keep wakeup
sources active during system suspend") and 744dddca ("clk:
renesas: mstp: Keep wakeup sources active during system suspend"), this
workaround is no longer needed.  Hence remove all explicit clock
handling to keep the device active.

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