staging: dwc2: remove redundant register reads

For calculating FIFO offsets, the sizes of preceding fifos need to be
known. For filling the GDFIFOCFG register, these fifo sizes were read
from hardware registers. However, these values were written to these
registers just a few lines before, so we can just use the values written
instead.

Signed-off-by: Matthijs Kooijman <matthijs@stdin.nl>
Acked-by: Paul Zimmerman <paulz@synopsys.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>