usbnet: smsc75xx: apply the introduced usbnet_{read|write}_cmd_nopm

This patch applies the introduced usbnet_read_cmd_nopm() and
usbnet_write_cmd_nopm() in the callback of resume and suspend
to avoid deadlock if USB runtime PM is considered into
usbnet_read_cmd() and usbnet_write_cmd().

Cc: Steve Glendinning <steve.glendinning@shawell.net>
Signed-off-by: Ming Lei <ming.lei@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>