usb: dwc2: Fix fifo_show() functionality

NPTXFIFO's start address is showing 0x03000000 instead of 0x00000800.
Replaced val & FIFOSIZE_DEPTH_MASK by val & FIFOSIZE_STARTADDR_MASK in
fifo_show() function.

Signed-off-by: Razmik Karapetyan <razmik@synopsys.com>
Signed-off-by: John Youn <johnyoun@synopsys.com>
Signed-off-by: Felipe Balbi <felipe.balbi@linux.intel.com>