net: sh_eth: Fix checkpatch warning

Fix minor checkpatch warning about udelay(3000) being too long
and should be replaced by mdelay(3).

Signed-off-by: Marek Vasut <marek.vasut+renesas@gmail.com>
Cc: Nobuhiro Iwamatsu <iwamatsu@nigauri.org>
Cc: Joe Hershberger <joe.hershberger@ni.com>