USB: dwc3-msm: Use maximum_speed as speed if no speed information

Speed is not notified in case of platforms having micro USB connector
instead of USB type C connector. In this case, use already set value
of maximum_speed as speed. maximum_speed can be set using devicetree
entry. If it is not set using devicetree entry, it is set as super
speed by default with dwc3_probe() API.

Change-Id: I6f29914ca9e2345157330651464b7a0c151f1f97
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>
Signed-off-by: Mayank Rana <mrana@codeaurora.org>