serial: xuartps: remove unnecessary register write

This writel writes the exact same value as the previous writel and is
thus unnecessary. It accidentally became unnecessary in e3538c37
("tty: xuartps: Beautify read-modify writes"), but the new behaviour is
now expected.

Link: https://www.spinics.net/lists/linux-serial/msg23168.html


Signed-off-by: Helmut Grohne <h.grohne@intenta.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>