ARM: dts: msm: Use correct regulator for SS USB

USB SS PHY uses the LDO28 regulator from PM8994, not
SMPS2. Fix the definition for the VDD supply.

Change-Id: I7d6f43c16d432c32200c265c7599c003d60dffbd
Signed-off-by: Jack Pham <jackp@codeaurora.org>