dwc3-msm: Return zero if max speed requested is already active

USB PD driver calls restart_usb_host_mode callback to start host mode
in high speed to release SS lanes.  If current maximum speed is same
as requested maximum speed i.e HIGH speed, then return zero instead
of ERROR to notify as success.

Change-Id: I45f3aaf4a8ecb85f0551e67fdc36263f6da50ed6
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>