usb: dwc2: gadget: consider all tx fifos

When matching tx fifo to endpoint, consider all fifos instead of
hard limiting to 8
Moreover, print error in case no fifo could be found.

Tested-by: Robert Baldyga <r.baldyga@samsung.com>
Acked-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Mian Yousaf Kaukab <yousaf.kaukab@intel.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>