usb: dwc2: Remove cat_printf()

cat_printf() implements the newly introduced seq_buf API.
Use the latter to save some line of code.

Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Link: https://lore.kernel.org/r/abf3d0361ea291468d121062207a766b0c3228f2.1710087556.git.christophe.jaillet@wanadoo.fr


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