imx: pmic: Set proper pmic name for iMX53 HSC|DDC boards

After the
commit 4213609c ("drivers: core: use strcmp when find device by name")
the exact DTS node name for PMIC device must be provided.

This patch fixes this issue by providing full DTS node name ('mc34708@8').

Signed-off-by: Lukasz Majewski <lukma@denx.de>
Reviewed-by: Jaehoon Chug <jh80.chung@samsung.com>