USB: serial: ftdi_sio: clean up printk format specifier

The latency is an unsigned int and should be printed as such (even if it
only holds values in the range 0..255).

Signed-off-by: Daniels Umanovskis <du@axentia.se>
Link: https://lore.kernel.org/r/20220426123714.2000-1-du@axentia.se


[ johan: amend commit message ]
Signed-off-by: Johan Hovold <johan@kernel.org>