can: etas_es58x: fix signedness of USB RX and TX pipes

USB pipes are meant to be unsigned int (c.f. [1]). However, fields
rx_pipe and tx_pipe of struct es58x_device are both signed
integers. Change the type of those two fields from int to unsigned
int.

[1] https://elixir.bootlin.com/linux/v5.18/source/include/linux/usb.h#L1571

Link: https://lore.kernel.org/all/20220611162037.1507-3-mailhol.vincent@wanadoo.fr
Signed-off-by: Vincent Mailhol <mailhol.vincent@wanadoo.fr>
Signed-off-by: Marc Kleine-Budde <mkl@pengutronix.de>