usb: dwc3: Increase the inter packet gap for USB 2.0

Default 0 value for IP_GAP_ADD_ON field of DWC3_GUCTL1
register is causing failure of EL_23 test. This value
corresponds to inter-packet gap of 182.163 ns. Increase
the value to 1 which corresponds to 199.794 ns. This
improves margin required to pass the test.

Change-Id: Iabc71a746ac90251eaec25597d8506df416796a5
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>