Fix synopsys fifo flush during stall
Fix synopsys fifo flush during stall

Wrong FIFO was flushed in dcd_edpt_stall().
(epnum - 1) should only be used when accessing DIEPTXF registers.

For DIEPCTL and GRSTCTL epnum is correct index.

hathach/tinyusb,hathach/tinyusb,hathach/tinyusb