usb: dwc3: change stream event enable bit back to 13

Commit ff3f0789 ("usb: dwc3: use BIT() macro where possible")
changed DWC3_DEPCFG_STREAM_EVENT_EN from bit 13 to bit 12.

Spotted this cleanup typo while looking at diffs between 4.9.35 and
4.14.16 for a separate issue.

Fixes: ff3f0789 ("usb: dwc3: use BIT() macro where possible")
Signed-off-by: Erich E. Hoover <ehoover@sweptlaser.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>