Use read-modify-write instead of a simple write to change the register
contents, to close existing the race window between the original manual
read and write.
Signed-off-by: NSascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: NMarc Kleine-Budde <mkl@pengutronix.de>
Acked-by: NWolfgang Grandegger <wg@grandegger.com>