usb: dwc3: gadget: Fix TXFIFO resize logic for non-zero EPs

Commit 93940d366f61f ("dwc3: gadget: Use TXFIFO register based
on used dwc3 version") incorrectly used EP-0's TXFIFO 'size'
as start address of TXFIFOs instead of using TXFSTADDR_N of
EP-0. This results in incorrect programming of TXFIFOs.
Fix this by using TXFIFOSIZ0s' TXFSTADDR_N (Bits 31:16) which
is same for both usb3 and usb31 version cores.

Change-Id: Iccc6b0b5560d6c460923f5ca62f6b1647d30c652
Signed-off-by: Manu Gautam <mgautam@codeaurora.org>