ARM: shmobile: r8a7740: Add interim sh-eth device name to clocks list

When we use the ethernet device via DT setup, we need to add it
to a lookup list until this is properly handled later in a DT-only
fashion.

Signed-off-by: Bastian Hecht <hechtb+renesas@gmail.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>