tty: serial: uartlite: Use read_poll_timeout for a polling loop

tty: serial: uartlite: Use read_poll_timeout for a polling loop

read_poll_timeout was recently introduced, and can be used to simplify
our console polling loop. This results in a slight reduction in code.
early_uartlite_putc can't get the same treatment, because it can be
called before udelay is set up.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Link: https://lore.kernel.org/r/20210826192549.3203071-1-sean.anderson@seco.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>