usb: max-3421: Fix setting of I/O pins

To update the I/O pins, the registers are read/modified/written. The
read operation incorrectly always read the first register. Although
wrong, there wasn't any impact as all the output pins are always
written, and the inputs are read only anyway.

Fixes: 2d53139f

 ("Add support for using a MAX3421E chip as a host driver.")
Signed-off-by: Mark Tomlinson <mark.tomlinson@alliedtelesis.co.nz>
Link: https://lore.kernel.org/r/20230207033337.18112-1-mark.tomlinson@alliedtelesis.co.nz
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>