usb: dwc3: correct the super speed check api

When the device operates in full speed mode, the CONNECTSPD field
vaue is 1. Using bitwise & operator on this value for super speed
check results in full speed being erroneously calculated as super
speed. Fix this by comparing the absolute value of CONNECTSPD for
super speed check.

Change-Id: I2bf497748f621b1982aecda55a9a280d93f84858
Signed-off-by: Elson Roy Serrao <eserrao@codeaurora.org>