USB / dwc3: Fix three doc-build warnings

Two kerneldoc comments in gadget.c have excess function parameter description or wrong
prototype name and one kerneldoc comment in core.c has an excess function parameter
description, resulting in these three doc-build warnings:

   1. ./drivers/usb/dwc3/gadget.c:675: warning: Excess function parameter
        'nfifos' description in 'dwc3_gadget_calc_tx_fifo_size'
   2. ./drivers/usb/dwc3/gadget.c:700: warning: expecting prototype for
        dwc3_gadget_clear_tx_fifo_size(). Prototype was for dwc3_gadget_clear_tx_fifos()
        instead
   3. ./drivers/usb/dwc3/core.c:347: warning: Excess function parameter 'ref_clk_per'
        description in 'dwc3_ref_clk_period'

Fix the warnings by correcting the prototype name and removing excess parameter descriptions.

Signed-off-by: Kushagra Verma <kushagra765@outlook.com>
Link: https://lore.kernel.org/r/SI2PR01MB392995043CACD80884A13764F81C9@SI2PR01MB3929.apcprd01.prod.exchangelabs.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>