usb: dwc3: gadget: fix mask and shift order in DWC3_DCFG_NUMP()

In the original DWC3_DCFG_NUMP() was always zero.  It looks like the
intent was to shift first and then do the mask.

Fixes: 2a58f9c1 ('usb: dwc3: gadget: disable automatic calculation of ACK TP NUMP')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>