soc: samsung: pm_domains: Use full names in subdomains registration log

Device tree none name for each power domain should be "power-domain", so
use a bit more descriptive full node name in messages about subdomain
registration. This way the following meaningless message:

power-domain has as child subdomain: power-domain.

is changed to a bit more meaningful one:

/soc/power-domain@105c40a0 has as child subdomain: /soc/power-domain@105c4020.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>