rockchip: rk3308: fix rockchip_dnl_key_pressed() on roc-cc

Commit 6aa4fe39 ("dm: core: Rename and fix uclass_get_by_name_len()")
changed uclass_get_device_by_name() to an exact match when previously it
behaved as a prefix match.

The roc-cc code relied on this prefix match by only specifying part of
the device name.  Fix this by using the full name including the address.

Signed-off-by: John Keeping <john@metanate.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>