usb: dwc3: gadget: Fix full speed mode

DCFG.DEVSPD == 0x3 is not valid and we need to set
DCFG.DEVSPD to 0x1 for full speed mode. Same goes for
DSTS.CONNECTSPD.

Old databooks had 0x3 for full speed in 48MHz mode for
USB1.1 transceivers which was never supported. Newer databooks
don't mention 0x3 at all.

Cc: John Youn <John.Youn@synopsys.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>