For better readability should this code be reviewed
in future, replace the hardcoded input numbers
with an enum.

This is just a cosmetic change and was verified
to not affect clk-imx6.o.

Reviewed-by: Philipp Zabel <p.zabel@pengutronix.de>
Tested-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: Ahmad Fatoum <a.fatoum@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>