colibri_imx7: provide proper node name to pmic_get

colibri_imx7: provide proper node name to pmic_get

Implementation of pmic_get() uses uclass_find_device_by_name(), which
behaviour was changed in 4213609cc7
("drivers: core: use strcmp when find device by name"). Now we have to
supply full node name with unit address.

Fixes boot issue:
U-Boot 2019.07-00788-g0ef6e69a1e-dirty (Jul 19 2019 - 15:27:02 +0300)

CPU:   Freescale i.MX7D rev1.3 1000 MHz (running at 792 MHz)
CPU:   Extended Commercial temperature grade (-20C to 105C) at 41C
Reset cause: POR
DRAM:  512 MiB
initcall sequence 9ffd3a4c failed at call 87803c61 (err=-19)
ERROR Please RESET the board

Fixes: 4213609cc7("drivers: core: use strcmp when find device by name")
Signed-off-by: Igor Opaniuk <igor.opaniuk@toradex.com>
Reviewed-by: Oleksandr Suvorov <oleksandr.suvorov@toradex.com>