usb: dwc3-msm: Fix bug in PHY reset sequence

When performing reset on the DWC3 controller's UTMI HSPHY
interface, only bit 31 of DWC3_GUSB2PHYCFG(0) should be
asserted. Fix the code which is incorrectly writing to
bits 28-31 and only clearing bit 31.

Change-Id: I4a2acf05974e7002f5592e8977eaab775342f57d
Signed-off-by: Jack Pham <jackp@codeaurora.org>