ARM: dts: exynos: Fix property values of LDO15/17 for Odroid XU3/XU4

Looking at the schematic, LDO15 and LDO17 are tied as a power source of a
builtin network chipset. Correct voltage on LDO15 to 3.3V and the name
of LDO17 to "vdd_ldo17".

Signed-off-by: Dongjin Kim <tobetter@gmail.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>