usb: pdphy: Widen voltage range setting for VDD regulator

The PDPHY is tolerant of a wide range for its VDD, between 2.8V
and 3.3V. Update the min/max values for regulator_set_voltage().

Change-Id: Ic49e4cc5b7159ed6a7393d13ec70f6b6318d3c57
Signed-off-by: Jack Pham <jackp@codeaurora.org>