tty: serial: uartlite: Use constants in early_uartlite_putc

Use the constants defined at the beginning of this file instead of
integer literals when accessing registers. This makes this code easier
to read, and obviates the need for some explanatory comments.

Signed-off-by: Sean Anderson <sean.anderson@seco.com>
Link: https://lore.kernel.org/r/20210826194323.3209227-1-sean.anderson@seco.com


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